Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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scoured using compressed air introduced through the

underdrain to break up compacted solids. Previously

filtered water is then passed upwards, at a velocity of

around 20 m h

1

for 10 min, to remove entrained

solids. Rapid gravity filtration is an important barrier

treatment for Cryptosporidium and Giardia, so close

attention is paid to conditions that may cause break-

through of solids into the filtered water. Improve-

ments in laser techniques to measure particle

numbers and size distribution have led to a greater

understanding of the correct coagulation conditions,

minimization of flow changes through filters, and the

ripening phase immediately after a backwash as im-

portant factors in controlling the numbers of oocysts

in the treated water. The dirty backwash water will

contain a higher concentration of oocysts than the

raw water and must be disposed of carefully. Often

this water is returned to the raw inlet, at a very low

dilution rate, following settlement to remove the

coagulant sludge.

0023 Slow sand filtration Slow sand filters are used with-

out the addition of coagulant. The lower velocities

used mean more particles are retained which in turn

encourages biological activity. Within days the layer

of organic material on the surface, known as the

schmutzdecke, becomes capable of removing color

and turbidity and large numbers of bacteria. Principal

mechanisms are straining and entrapment but diges-

tion of dissolved organics also takes place by a variety

of organisms, such as protozoa, algae, and bacteria

living in the schmutzdecke. A comparison of rapid

and slow and filtration is shown in Table 4. Slow sand

filters are cleaned by removing the surface layer of

sand and schmutzdecke.

0024Membrane filtration Membrane filtration has been

in use in the food industry for some decades. Very fine

filtration generates a relatively high pressure but pro-

duces a very-high-quality product. More recently, im-

provements in the membrane-manufacturing process

and a growing market have made the technology

more cost-effective. Increasing public concern over

Cryptosporidium, a chlorine-resistant, spore-forming

organism that can cause severe illness, has resulted in

membranes being installed as one of the few effective

treatments.

0025Iron and manganese removal Many groundwater

sources can be found that are of good microbiological

quality but esthetically unsuitable because of high

concentrations of iron and manganese salts res-

ulting in black or brown discolored water. These

waters can be successfully treated using filtration

techniques. However, the metal salts must be in

an insoluble, particulate form to be removed effect-

ively. Soluble metal ions can be converted to particu-

late forms by oxidation using aeration, chlorination,

or ozone. Due to their relative oxidizing power,

oxidation can be achieved in minutes with ozone

but may take hours with air. Removal of manganese

requires a longer reaction time or a stronger oxidant

than iron; potassium permanganate or ozone is

often used. The oxidation reaction kinetics are

dependent on pH and best performed at around

pH 8.0.

Organics Removal

0026The UK and Europe have treatment- and health-

related standards for various organic compounds.

Contamination can occur from both agricultural and

industrial sources. Soluble organic compounds such

as herbicides, particularly triazines, chlorophenoxy

Backwash

outlet

Gravel

Filter

outlet

Flow

control

valve

Backwash

inlet

Filter

inlet

Water level

during washing

Water level

during filtering

Underdrain

system

Sand

fig0001 Figure 1 Schematic diagram of a rapid gravity filter.

tbl0004 Table 4 Comparison of rapid and slow sand filtration

Parameter Rapid gravity/pressure Slow sand

Filter media Sand, granular-activated carbon or anthracite Sand

Filtration rate (m h

1

) 3–10 0.2

Filter run length 24 h 60 days

Cleaning Air scour and upwash Surface skim

Mechanism Physical entrapment in media depth Physical entrapment on media surface, biological digestion

Pretreatment Almost always used with coagulation Microstraining or roughing filtration

WATER SUPPLIES/Water Treatment 6109

acids, and urons, are often found. Industrial solvents,

carbon tetrachloride, and trichloroethene (TCE) can

also be found to contaminate groundwater. Coagula-

tion and filtration techniques are ineffective but ozo-

nation, granular-activated carbon, and air stripping

can be used to remove these contaminants.

0027 Ozone will degrade many pesticides and other

organics. Concern for the health effects of the degrad-

ation products and the potential for bacterial re-

growth mean it is often used with granular-activated

carbon to absorb the degraded organics.

0028 Granular-activated carbon (fixed bed) will absorb

a number of organic compounds and is commonly

used for pesticide removal and for the removal of

taste- and odor-causing compounds. It can also be

used as a rapid gravity filtration medium, thus

combining two processes in one. The carbon has a

finite lifetime and, depending on the organic loading

and type, will require regeneration. This involves

returning the medium to the manufacturer to undergo

a high-temperature regeneration process to oxidize

the adsorbed organic compounds.

0029 Powdered activated carbon can have similar uses

but is dosed into a contact tank or similar structure

and is subsequently removed by a downstream separ-

ation process such as filtration.

Removing Dissolved Salts

Nitrate Removal

003 0 Increasing levels of nitrate in groundwater sources

are generating a need for nitrate removal plant in

the UK and Europe. Ideally, the problem is best

approached by reducing the levels at source, by

minimizing the levels of nitrate applied to the land

within the water catchment area. There are, in the

UK, government-aided grants to identify and assist

farmers in controlling the application of nitrate

fertilizers.

0031 Where treatment is required, ion exchange and

electrodialysis have been used in the past. The princi-

pal of ion exchange is to pass the water through a

bed of synthetic resin beads, which exchange nitrate

ions for chloride. Once the resin is saturated with

nitrate, it is regenerated with brine and a waste prod-

uct containing high concentrations of nitrate and sul-

fate is produced. Electrodialysis, which is also

commonly used for desalination of brackish and sea

water, involves applying an electrical current across a

membrane that is capable of selectively passing ni-

trate ions but not water. More recently, with improve-

ments in membrane manufacture, reverse osmosis

is becoming a cost-effective solution for nitrate

removal.

Softening

0032Softening is not extensively used in the UK water

industry but is used to protect industrial boilers

from scaling. Precipitation using lime can be used to

precipitate calcium and magnesium. This process pro-

duces large quantities of sludge. Alternatives are ion

exchange and, more recently, reverse osmosis. Ion

exchange resins will replace calcium and magnesium

ions for chloride ions and, once saturated, they can be

regenerated using brine.

Distribution Systems

Water Quality in Distribution Systems

0033Water that has been treated at the treatment plant can

take days to reach the customer through the under-

ground distribution network of pipes and service res-

ervoirs. To insure that the quality and especially the

microbiological safety of the water do not deteriorate

on the way, residual disinfectant, pH stabilization,

and other corrosivity control processes are used at

the treatment works.

0034A free chlorine residual concentration of around

0.3mg Cl

1

will insure bacterial regrowth will not

occur for several days. This will however depend on

the distance and time of travel, the water tempera-

ture, as chlorine will decay more quickly at higher

temperatures, the condition and age of the distribu-

tion network, and the quality of the water. If the

water contains THM precursors, the additional con-

tact time with chlorine in the distribution network

can lead to higher concentrations of THMs reaching

the customer’s tap than found at the treatment works.

Corrosion Control

0035The chemical balance between carbonates and bicar-

bonates is especially important in corrosion control.

A protective layer of calcium carbonate will form on

the inside of distribution pipes if the water is ad-

equately stabilized. This requires the balance of free

carbon dioxide, carbonate, and bicarbonate concen-

trations to be controlled, usually by adjusting the pH

to control Eqn (2).

þ CaCO

þ H

O ¼ CaðHCO

ð2Þ

Excess carbon dioxide will dissolve calcium carbon-

ate, and cause corrosion to distribution pipework.

Carbon dioxide is an acidic gas. If it is removed, for

example in an aeration process, it is likely that the

pH of the water will rise and calcium carbonate

will be precipitated. The corrosivity of water can

be estimated using corrosion indices; the most

commonly used index is the Langelier saturation

6110 WATER SUPPLIES/Water Treatment

index. The saturation pH is calculated from ionic

strength, calcium, alkalinity, and temperature and

compared to the measured pH of the water. A positive

index indicates the water will precipitate calcium

carbonate and a negative index shows that it has

corrosive potential. The index can therefore be con-

trolled by adjusting the pH, commonly with lime, as

this has the advantage of also adding calcium which

reduces the saturation pH. Mineral acid or caustic

soda is also used.

0036 Lead plumbing was extensively used in the UK at

the turn of the 19th century, but concern over very

low levels of lead contamination have prompted the

need to replace pipework wherever possible and con-

trol lead solubility. This is achieved by dosing phos-

phoric acid to around 0.2–2.0mgPl

1

as the water

enters the distribution network from the treatment

works. A protective coating of lead phosphate is

formed which reduces the concentration of lead in

the water.

Plant Design

0037 In summary, the aim of the design of a water treat-

ment plant will essentially address the following

criteria:

0038 Establish the difference in quality of the raw

source compared to the required treated water

quality.

0039 Specify process plant, and its operating limita-

tions, capable of producing sufficient quantity

and quality to meet customer demand and legisla-

tive requirements.

0040 Place the plant geographically to insure minimal

cost of transport and potential for quality deterior-

ation.

0041 Provide a treatment solution at an acceptable

capital and operating cost.

Seealso: Filtration of Liquids; Iron:Propertiesand

Determination; Manganese; Membrane Techniques:

PrinciplesofUltrafiltration;ApplicationsofUltrafiltration;

Nitrates and Nitrites; Pesticides and Herbicides:

ResidueDetermination;Toxicology; Water Supplies:

ChemicalAnalysis;MicrobiologicalAnalysis

Further Reading

Badenoch J (1990) Cryptosporidium in Water Supplies,

p. 230. UK: DETR.

Barrett JM, Bryck J, Robin Collins M, Janonis BA and

Logsdon GS (1991) Manual of Design for Slow Sand

Filtration, pp. 5–12, AWWA Research Foundation.

Bouchier I (1998) Cryptosporidium in Water Supplies. UK:

DETR.

Carrol T and Booker N (2000) Membrane Technology in

Water and Wastewater Treatment, pp. 93–99. Royal

Society of Chemistry.

Drinking Water Inspectorate website. Available online at

www.dwi.gov.uk.

Environment Agency web site. Available online at environ-

ment–agency.gov.uk.

Hall T and Hyde RA (eds) (1992) Water Treatment

Processes and Practices. Swindon: WRC.

Hammer MJ (1986) Water and Wastewater Technology,

2nd edn. New York: John Wiley.

Kirmeyer GJ et al. (1999) Maintaining Water Quality in

Finished Water Storage Facilities, pp. 137–168. AWWA

Research Foundation.

Langlais B, Reckhow D and Brink D (1991) Ozone in Water

Treatment Application and Engineering, pp. 31–54.

Lewis.

Montgomery J (1985) Water Treatment Principles. New

York: John Wiley.

National Rivers Authority (1992) The Influence of Agricul-

ture on the Quality of Natural Waters in England and

Wales, 1st edn, pp. 19–23. Bristol: National Rivers

Authority.

Pontius FW (1990) Water Quality and Treatment, pp.

269–361. Mc-Graw-Hill.

Twort AC, Law FM, Crowley FW and Ratnayaka DD

(1994) Water Supply, 4th edn, pp. 258–277. New

York: John Wiley.

World Health Organization (1993) Guidelines for Drinking

Water Quality, 2nd edn, pp. 93–106. France: World

Health Organization.

Chemical Analysis

P J Walker, Thames Water Utilities Ltd, UK

Introduction

0001Most of the water supplied for human consumption

has to comply with national or international stand-

ards with regard to its chemical composition and the

concentration of material present. The limits placed

on the permitted concentrations of these compounds

are not always health-based; some may be set for

esthetic reasons or they may be limited by the practi-

calities of the analytical methods, limit of detection at

the time of setting. Chemical analysis of water will

provide information about compliance with these

standards. It will also assist treatment plant operators

to insure that the production processes are working

efficiently and that the purity of the water is main-

tained within the distribution system.

0002The World Health Organization (WHO) regularly

updates and issues drinking-water quality guidelines

WATER SUPPLIES/Chemical Analysis 6111

with the aim of protecting public health and forming

the basis for national water quality criteria. National

policy may vary between countries and as a result

there are often differences between the limits

expressed in the WHO guidelines and those in the

national legislation.

0003 In addition to concentration limits, it is becoming

more common for national legislation to specify that

a quality system must be in place to insure that the

results of chemical analysis are valid. Validity in this

sense usually means:

0004 The performance of the analytical method is

known and documented for the sample type

0005 This performance complies with regulatory criteria

for limit of detection, systematic, and random error

for both analytical standards and samples

0006 There is documented evidence that there is a system

of monitoring instrumental performance and

analyst training, and use of formalized methods

0007 Analytical quality control (AQC) standards are

routinely used as additional samples

0008 There is regular participation in recognized analyt-

ical proficiency schemes.

A system where quality control is specified will insure

that results from different laboratories can be com-

pared or used in national statistical exercises.

0009 Laboratory standard methods of analysis are pub-

lished by national agencies e.g., US Environmental

Protection Agency (EPA), and the Environment

Agency in the UK. They are also produced by the

International Standards Organization (ISO), the CEN

standards body in Europe, national standards bodies,

e.g., BSI and DIN, and also professional bodies such

as the American Public Health Association.

Sampling

0010 It is essential that sampling is performed correctly.

Failure to sample properly will affect the result and

invalidate it. A sample must be representative of the

bulk material, it must be taken into the correct con-

tainer, with an appropriate preservative if required,

and the sample container must be clearly and

unambiguously labeled.

0011 The sampling procedure is dependent on the analy-

sis required. In most circumstances the sample must

be representative of the drinking water delivered

to the sample point. To achieve this the water is

allowed to flow to waste for a suitable ‘flushing

period’ to clear any nonrepresentative water in the

pipes from the supply main to the sampling point.

The exception however is when lead analysis is to

be carried out. It is essential that the sample collected

is representative of the water that has been in

prolonged contact with the pipework and any

plumbing metals associated with it. In these circum-

stances no flushing occurs as the sample is drawn

directly from the sampling point into the sample

container.

0012The sample container must not affect the sample by

adsorption, absorption, or contribution, e.g., leach-

ing or carry-over from previous samples. Glass was

the preferred material for sample containers, but the

newer plastic materials, e.g., polyethylene teraphtha-

late (PET), are replacing glass in many circumstances.

Metals, inorganics, and some pesticide determinands

have all been shown to be stable within plastic

bottles. Compared to glass the advantages of plastic

bottles are that they are light-weight, more robust,

inexpensive, and disposable. Quality control becomes

easier in insuring bottle cleanliness as a small repre-

sentative sample from each delivered batch can be

checked before use. As the bottles are used once

only and then discarded, there is no problem with

carry-over from the previous sample.

0013Special care has to be taken if the analyte can

undergo degradation or reaction between the time

of sampling and start of analysis. Most samples are

preserved by refrigeration, but dissolved oxygen, sul-

fide, and polynuclear aromatic hydrocarbons (PAH)

all require ‘fixing’ on-site at the time of sampling.

Mercury can be lost prior to analysis and is usually

preserved with nitric acid and/or potassium dichro-

mate. Recent work has shown that the addition of

gold solution up to 5 mg l

1

Au has excellent preser-

vation properties for both glass and plastic (PET)

containers. This works well with inductively coupled

plasma – mass spectrometry (ICP-MS), but signifi-

cantly depresses the signal from a cold vapor fluores-

cence instrument system.

Basic Characterization

0014By using a suite of simple tests it is possible to

characterize water. These tests are pH, electrical con-

ductivity, color, turbidity, alkalinity, and hardness.

Additionally, where drinking water has been disin-

fected with chlorine, the determination of free and

combined chlorine is also determined. The organolep-

tic properties of taste and odor also provide useful

monitoring data.

0015This determinand indicates the acidity or alkalinity of

the water. It is measured using a pH meter connected

to an electrode combination that is responsive to pH.

Calibration utilizes standard pH buffer solutions over

the required range. It is usual to supply drinking

6112 WATER SUPPLIES/Chemical Analysis

water in the range pH 6.0–9.5. Water supplied out-

side this range is increasingly corrosive.

Electrical Conductivity

0016 The electrical conductivity of drinking water is meas-

ured using a pair of electrodes set a specific distance

apart. The conductivity of the water is dependent

upon the number and type of ions present and will

also indicate the amount of dissolved material present

in the sample. The meter is calibrated using a stand-

ard solution of potassium chloride.

Color

0017 The unit of color is defined by the platinum cobalt

method, being the color produced by 1 mg l

1

plat-

inum as chloroplatinate ion. There is a direct relation-

ship with the Hazen scale.

0018 Color is measured using visual comparison against

liquid standards, calibrated colored glass disks, or

spectrometrically. With spectrometry the wavelength

used determines the result.

0019 The Hazen scale is primarily used in nonlaboratory

situations. It comprises a range of colored glass disks,

calibrated in color and intensity to match the

chloroplatinate colorimetric test. The sample is

poured into a viewing tube and matched to the

Hazen standard against a white background. A var-

iety of manufacturers produce these calibrated glass

disks; ranges of 0–70 mg Pt l

1

are common. The

chloroplatinate method involves the preparation of

the standard colors from potassium chloroplatinate

standard solution.

0020 Color in water is mainly due to free sediment, iron

or manganese material, organic matter, and industrial

pollutants, e.g., dyes.

Turbidity

0021 This determinand is a measure of the clarity of the

water. It is usual to measure turbidity in formazin

turbidity units (FTU), following calibration. A variety

of techniques exist to measure turbidity but the most

popular uses nephelometry, where the intensity of

scattered light is measured. It is usual to have the

detection at 90



to the light source.

Alkalinity

0022 This general term covers the combined concentra-

tions of hydroxide, carbonate, and bicarbonate

present in the sample. Actual concentrations are

dependent upon pH, temperature, and total dissolved

solids content. A series of nomograms are used to

calculate actual concentration.

0023 Alkalinity is determined either colorimetrically or

by titration with acid.

Hardness

0024Calcium and magnesium salts present determine the

hardness of the water. Permanent hardness (noncar-

bonate hardness) is due to the presence of chlorides,

sulfates, and nitrates. Carbonate hardness is due to

carbonate and bicarbonate salts of calcium and

magnesium.

Metals Analysis

0025A variety of instrumental techniques and colorimetric

methods can be used to detect metallic elements. Elec-

trochemical systems, i.e., anodic striping voltametry,

atomic absorption – flame or furnace – inductively

coupled plasma-optical (OES) or mass spectrometry

(MS) are all practical instrumental systems. The

correct choice of system is dependent upon:

0026limit of detection required

0027number of samples to be analyzed

0028number and type of metal analyses per sample

0029degree of automation required

0030skill required of analyst

The lowest limits of detection (LoDs) are most likely

to be achieved by the use of an ICP-MS, which, when

used with an autosampler system, has the potential to

analyze large numbers of samples for most metals/

metalloids unattended.

0031However, with ICP-MS, problems arise with

sodium, potassium, calcium, and magnesium due to

their high concentration in drinking water, and also

with a range of interferences developed within the

plasma. Use of gold with matrix-matched standards

(Na, K, Ca, Hg) allows the determination of mercury

(Hg), arsenic (As), selenium (Se), and antimony (Sb).

The use of an ultrasonic nebulizer (USN) or special-

ized nebulizers (e.g., Minehardt) can significantly

improve the performance of an ICP-OES instrument,

resulting in lower LoDs than the conventional instru-

ment alone. Many ICP-OES instruments have true

simultaneous detection for many metals by the

incorporation of charge-coupled arrays or similar

devices within the detector unit.

0032Electrochemical methods such as anode striping

voltametry can produce results with good precision

and low LoDs but they are disadvantaged by being

slow compared to ICP use. Improvements have been

made by automating sample analysis and the use of

multiplace sample holders, but they are not in

common use in high-throughput situations.

0033Mercury, arsenic, selenium, and antimony can be

detected using an ICP-MS, but most other flame or

plasma systems cannot produce acceptable LODs or

precision for these elements. Furnace systems can get

low LoDs by multiple additions of analyte to the

WATER SUPPLIES/Chemical Analysis 6113

pyrolizing component, but this is a slow technique.

Mercury is frequently analyzed using the cold vapor

fluorescence technique. In this a reducing agent, i.e.,

stannous chloride or sodium borohydride solutions,

reduces the inorganic mercury to its elemental form in

solution. Bubbling a gas, usually argon, through this

solution strips out the elemental mercury vapor. De-

tection is usually by fluorescence, although absorption

and other systems have been used. Arsenic, antimony,

and selenium can be converted to corresponding hy-

drides by reaction with sodium borohydride solution.

These volatile forms can then be directed to flame or

optical systems for detection. It is vital to insure that

the element of interest is in the appropriate oxidation

state, As

III

Sb, Se

, prior to hydride formation. Use of

an inappropriate oxidation state will lead to a low

result or no result being obtained.

0034 In addition to occurring naturally, aluminum salts

can be used within the water treatment process to

assist coagulation and subsequent settlement. With a

WHO limit of 200 mgl

1

, aluminum can be analyzed

colorimetrically or instrumentally. However alumi-

num in drinking water can have a detrimental effect

on kidney dialysis at concentrations as low as 20 mgl

1

Al. Any method chosen for aluminum should be

capable of detecting this concentration where kidney

dialysis patients are treated in the supply area.

0035 The metals present in high concentrations –

sodium, potassium, calcium, and magnesium – can

be determined using flame photometry in addition to

flame absorption or ICP-OES.

0036 WHO guidelines for metals are given in Table 1.

Anion Analysis

0037 Ion-selective electrodes, ion chromatography, and

many forms of automated and manual colorimetric

techniques are used to analyze anionic compounds.

Automated methods include air-segmented and flow

injection analyzers or discrete systems derived from

clinical analyzers. The choice of technique is depend-

ent upon daily sample numbers and range of analysis

required.

Ammonia, Nitrite, and Nitrate

0038These nitrogen-based ions can be determined using all

of the above techniques. The calculation of nitrate is

usually obtained by subtracting the nitrite result from

that of total oxidized nitrogen (TON). Total oxidized

nitrogen is determined by the selective reduction of

nitrate to nitrite and its determination as nitrite, along

with any nitrite in the sample.

Chloride

0039Chloride can be analyzed by all the above methods

plus titration with silver or mercuric nitrate solution.

Colorimetric analysis is based on the reaction that

liberates thiocyanate ions from mercuric thiocyanate

solution. In the presence of iron III ions, the highly

colored ferric thiocyanate is formed and this is

measured at 480 nm.

Fluoride

0040Fluoride may occur naturally or may have been added

to reduce the occurrence of dental caries. It can be

analyzed by all the above techniques.

Sulfate

0041This ion is usually determined using gravimetry and

turbidity following reaction with barium chloride so-

lution to form insoluble barium sulfate. Ion chroma-

tography is also used, as is the colorimetric methyl

thymol blue method.

Phosphates

0042Phosphates exist in a variety of forms in water. The

simplest form is orthophosphate, with the increas-

ingly more complex pyro-, meta-, poly-, and organo-

phosphates occurring less frequently and at lower

concentrations. Apart from the determination of

total phosphorus by ICP, separation into type is

dependent upon conversion to soluble orthopho-

sphate by increasingly more vigorous acid/hydroly-

sis/digestion. Subsequent colorimetric determination

of the orthophosphate using the vanodomolybdopho-

sphoric acid method, stannous chloride method, or

ascorbic acid method is dependent upon the expected

orthophosphate concentration.

tbl0001 Table 1 World Health Organization guidelines for metals

present in water

Aluminum 200 mgl

1

Antimony 5 mgl

1

Arsenic 10 mgl

1

Barium 700 mgl

1

Boron 300 mgl

1

Cadmium 3 mgl

1

Chromium 50 mgl

1

Copper 2000 mgl

1

Iron 2000 mgl

1

Lead 10 mgl

1

Manganese 500 mgl

1

Mercury 1 mgl

1

Molybdenum 70 mgl

1

Nickel 20 mgl

1

Selenium 10 mgl

1

National limits exist for beryllium, calcium, magnesium, silver, sodium,

tin, and zinc.

6114 WATER SUPPLIES/Chemical Analysis

Process Byproduct Analysis

0043 The most familiar process byproducts are the for-

mation of the trihalomethane group of organic

compounds following the reaction of chlorine with

organic material in the water supply. These com-

pounds (chloroform, bromodichloromethane, dibro-

mochloromethane, and bromoform) are normally

analyzed by head space gas chromatography using

an electronic capture detection (GC-ECD). Other

systems, e.g., purge-and-trap (P&T) and GC-MS,

have been used.

0044 The more frequent use of ozone as a pretreatment

prior to activated charcoal for the removal of com-

plex pesticides has established a need to analyze for

bromates, chlorates, and chlorites. These compounds

can be formed from the reaction of the ozone

with bromide and chloride ions in the supply water.

Ion chromatography, usually using a concentration

column, is the preferred method of detecting these

compounds. A new procedure, which appears to

offer very good LoDs, is currently being adopted. It

uses postcolumn derivatization with ultraviolet detec-

tion with the advantage that all compounds of inter-

est can be analyzed from the same sample injection.

Existing methods for bromate require a multistage

preparation to remove interfering chloride and sulfate

ions. Samples prepared in this way are analyzed using

differing chromatographic conditions. For these

reasons it is necessary to analyze bromate separately.

Organics Analysis

0045 A large number and range of compounds fall within

this area of analysis. They vary from simple molecules

to large complex compounds with differing stabilities

and solubilities. It is unrealistic to expect one instru-

ment to analyze the whole range of these compounds.

The current techniques used are specifically targeted

to obtain the best detection performance. Preferred

techniques readily utilize technical advances in instru-

mental techniques, as these become commercially

available.

0046 When analyzing for organic compounds present at

very low concentrations in water, the first stage of

analysis is usually the concentration of the analytes to

be determined. Concentration is achieved either by

extracting the compound(s) of interest into another

solvent – liquid/liquid extraction (LLE) – or on to a

specially prepared inert or polymeric material – solid-

phase extraction (SPE). In LLE the choice of solvent is

critical. It must not interfere with compound(s) being

concentrated, nor must it affect the chromatography

by obscuring the peaks of interest with the solvent

peak. Once extracted, the solvent phase is usually

reduced in volume by either evaporation under a

gentle flow of inert gas, e.g., nitrogen, or using

specialized equipment, such as the Kuderna Danish

evaporator.

0047Where a complex mixture of compounds is being

extracted, the relative solubilities and absorption cap-

abilities of each component can differ significantly.

These fundamental differences will lead to unequal

extraction ratios occurring which, unless corrected,

will lead to errors later in the analysis. It is normal in

these circumstances to evaluate the analysis of each

compound independently so that the percentage

extraction ratio is understood for each matrix type.

Once the information is available then the constancy

of extraction can be monitored by the addition of

surrogate standards to each sample prior to extrac-

tion. Surrogate standards are usually compounds very

similar to the target analyte, differing either by the

inclusion of a different substituted chemical group

within the molecule, or by the use of deuterated com-

pounds where mass spectrometry is used in the final

analysis. By appropriate choice of surrogate standard,

the range of extraction efficiencies can be monitored

during the extraction and corrected for in the final

result.

0048Internal standards are standards that are added to

the extracted material or concentrate and are used

to monitor the constancy of the analytical instru-

ment system used. The addition of compound(s) to

the extracted material enables the analyst to correct

for both random and systematic variations, e.g.,

partially blocked/worn injection systems, tempera-

ture variation, loss of column efficiency, and detector

deterioration.

0049The instrument systems used rely on chro-

matographic separation using either GC or high-

performance liquid chromatography (HPLC).

Different detectors are used according to the sensitiv-

ity required, but the reduced size and cost of mass

spectrometer detectors has led to their increased use,

particularly when deuterated compounds are used for

surrogate or internal standards. Large libraries of

‘most significant masses’ for organic compounds

have been compiled to assist the analyst to identify

compounds when using single-ion mode(s) (SIMs) of

MS-detector operation. Two or more ‘significant

masses’ can be used specifically to identify and quan-

titate a compound, particularly when it has one mass

fragment value that is identical to those produced by

other different compounds. The use of total ion count

(TIC) mode on an MS-detector will produce a more

conventional chromatogram of the separation, show-

ing peak height against time.

0050Typical organic compounds determined are de-

scribed below.

WATER SUPPLIES/Chemical Analysis 6115

Phenols

0051 These compounds have detectable tastes at low con-

centrations and may react with chlorine to produce

chlorophenols which have even lower taste thresh-

olds. They are analyzed by LLE using methylene

chloride and detected by GC using FID, ECD, or

MS detectors as appropriate. Derivitization using

pentafluorobenzylbromide produces lower detection

limits.

Trihalomethanes (THMs)

0052 These are normally produced when chlorine reacts

with naturally occurring humic or fulvic material

during disinfection. Industrial contamination can add

THM and other chlorinated hydrocarbons to the raw

water. THMs are analyzed by head space or P&T

techniques, followed by GC-ECD or GC-MS.

Pesticide Residues

0053 Organochlorine (OCP) or organophosphorus (OPPs)

can be analyzed together with polychlorinated bi-

phenyls (PCBs) using methylene chloride LLE and

GC-ECD or GC-MS instruments.

Phenoxy Acid Herbicides

0054 MCPB and 2.4.D are analyzed for by extraction into

diethylether and derivitized using diazomethane to

produce their methyl ethers. Analysis of the derivi-

tized compounds is by GC-MS.

Triazine and Uron Herbicides, Including Atrazine,

Diuron, and Prometryn

0055 These compounds tend to be thermally unstable and

are best suited to analysis using liquid chromatog-

raphy-MS detection following either methylene chlor-

ide LLE or solid-phase extraction using cartridges

preprepared for this specific extraction.

Polynuclear Aromatic Hydrocarbons

0056 This class includes the most frequently found com-

pound – fluoranthene – and the most toxic – ben-

zo(a)pyrene. The presence of these compounds is

mainly due to the coal tar pitch lining applied to

water distribution pipes. The limits applied to these

compounds are health-related. Analysis is by HPLC.

Organic Carbon

0057 This empirical determinand is frequently used as a

coarse monitor of quality in both supply and treated

water. There are many different techniques for analy-

sis, including combustion furnace or chemical oxida-

tion, with or without ultraviolet light to give carbon

dioxide, and reducing conditions to give methane.

The detection system is appropriate to the preparative

stage, e.g., infrared detectors for CO

and FID for

methane. The term ‘total organic carbon (TOC)’ is

the summation of the various forms of organic carbon

capable of being distinguished by differing prepara-

tive stages.

0058Dissolved organic carbon (DOC) – not retained on

a 0.45-mm filter

0059Particulate (POC) – the fraction retained as 0.45-

mm filter

0060Purgeable or volatile (VOC) – the fraction re-

moved by gas stripping

0061Nonpurgeable (NPOC) – the residue after gas

stripping

Radioactivity

0062The determination of radioactivity is sometimes re-

quired due to geological or artificial circumstances. It

is rare for there to be a requirement to investigate

specific radiochemical isotopes, although the moni-

toring of gross a- and gross b-emitters is used for

establishing and monitoring trends. WHO recom-

mends a limit of 1 Bq l

1

for a- and 100 Bq l

1

for

b-emitters. (A becqueral (Bq) is one disintegration per

second.)

0063Samples can be analyzed directly or in most cases

concentrated by boiling. Boiling removes any radon

present so this must be determined separately. Final

sample preparation is dependent upon the limit of

detection required and the instrument/detector used

to count the sample. Counting times vary between 3

and 10 h.

Quality Control

0064Quality control is very important if the results

obtained are to be credible and useful for comparison.

Analytical quality control is only a part of the total

system which should include information on the

actual performance of the instrument system used at

the time of analysis, the status of the analyst, i.e.,

trained or under training, the performance of the

technique on various sample types or matrices, and

the conditions under which the analysis was made.

0065The methods used to establish and maintain ana-

lytical quality control include the use of standards as

samples, analysis of duplicates, measures of drift, and

others, as appropriate. These values are plotted on

charts which show when the analysis is moving away

from the target value in a regular way or when the

results are outside the statistically established method

performance. Shewhart and cusum charts are both

used to determine if a procedure is within or outside

control.

6116 WATER SUPPLIES/Chemical Analysis

Seealso: Aluminum (Aluminium):Propertiesand

Determination; Chromatography:High-performance

LiquidChromatography;GasChromatography; Fluoride;

Legislation:InternationalStandards; Nitrates and

Nitrites; Pesticides and Herbicides:Residue

Determination; Phenolic Compounds; Phosphorus:

PropertiesandDetermination; Polycyclic Aromatic

Hydrocarbons; Quality Assurance and Quality

Control; Water Supplies:WaterTreatment; World

Health Organization

Further Reading

American Public Health Association (1998) Standard

Methods for the Examination of Water and Wastewater,

20th edn. American Public Health Association.

Fatemian, Allibone and Walker (1999) Analyst 124:

1233–1236.

Fatemian, Allibone and Walker (1999) Journal of Analysis

and Atomic Spectrometry 14: 235–239.

HMSO (1976–1992) Index of Methods for the Examin-

ation of Waters and Associated Materials. London:

HMSO.

World Health Organization. www.who.int

Microbiological Analysis

C Fricker, CRF Consulting, Reading, UK

Introduction

0001 The dramatic reduction in disease associated with the

consumption of drinking water over the last century

has been brought about largely by increased aware-

ness and by the considerable advances made in

treatment, disinfection, and distribution of potable

supplies. The microbiological and chemical examin-

ation of water plays an important part in the control

of water treatment processes. Microbiological exam-

ination of potable water is performed to insure the

safety of supply. In general, the tests used are based on

indicator organisms, the presence or absence of which

provides a measure of the microbiological quality of

water. This article deals with aspects of microbio-

logical examination of water from sampling through

to detection of some organisms that are important

pathogens for human beings.

Sampling and Handling of Samples

0002 Sampling issues have tended to receive less attention

than water quality issues in the various standards and

regulations that have been laid down. The recom-

mended frequency of sampling varies widely between

different regulatory authorities. In designing a micro-

biological monitoring program, the major consider-

ation is of course the health of the consumer. The

program should be designed to take account of the

size of the distribution network and should insure

that samples are taken from all areas of the network.

The frequency with which a particular supply needs

to be sampled depends primarily on the number of

consumers it supplies; the higher the number of con-

sumers, the more frequently sampling should take

place.

0003An ideal sampling regime should be completely

randomized. However, owing to the complexity of

many distribution systems, this is seldom possible.

For this reason, stratified random sampling is prob-

ably the best approach. The entire distribution should

be divided into discrete areas such that it is composed

of regions where contamination could occur without

being detected by sampling other areas. However,

whilst this approach may be ideal in theory, it is

seldom, if ever, adopted. In general, the sampling of

potable water supplies begins with the water entering

the distribution system. Samples from large water

treatment plants are usually taken on a daily basis,

whilst at smaller works regular monitoring of re-

sidual chlorine levels, together with less frequent

microbiological checks, is often used. In addition to

samples of water entering the supply, other sites such

as service reservoirs and break-pressure tanks are

regularly sampled. Samples from distribution are ran-

domized as much as possible and this also involves

sampling from consumers’ premises.

0004The type of sample taken depends on the reason for

sampling. Generally bacteriological sampling (for de-

tection of Escherichia coli and coliforms) involves the

collection of a relatively small volume of water (300–

500 ml), whereas samples for detection of specific

pathogens such as enteroviruses, Cryptosporidium,

Giardia and Salmonella involve larger volumes (10–

1000 l). Samples for bacteriological and virological

analysis require sterile bottles and the addition of

sodium thiosulfate. The sodium thiosulfate is used

to neutralize the effects of free chlorine in the water

sample. Samples for parasites such as Cryptosporid-

ium and Giardia may be taken by passing large

volumes of water through cartridge filters and

the filters are then taken to the laboratory for exam-

ination. Alternatively, smaller volumes of water

(10–100 l) may be collected into containers and trans-

ported to the laboratory for subsequent concentra-

tion. Microbiological samples should be examined

as soon as possible after collection. This is particu-

larly important for samples for bacteriological and

virological examination, where ideally samples

should be analysed within 6 h.

WATER SUPPLIES/Microbiological Analysis 6117

Colony Counts

0005 Water contains a variety of bacteria that may have

different temperature optima. Bacteria whose natural

habitat is cold water will, in general, have a lower

optimal growth temperature than those that enter

the water distribution system as contaminants. The

temperatures most often employed for providing

colony counts on potable water are 22



C and 37



Generally, plate counts are performed as pour plates

where a small amount of water (usually 1 ml) is trans-

ferred by pipette into a Petri dish and molten agar (at

about 47



C) is added. After mixing, the agar is

allowed to solidify and the plates are incubated at

the appropriate temperatures for 1–7 days before the

colonies are counted. The agar medium used varies

between different laboratories, but a general-purpose

medium such as yeast extract agar is most often

employed, although the less nutritious R

A is becom-

ing more widely used, as it usually allows detection of

a higher number of bacteria. It is sometimes necessary

to prepare serial 10-fold dilutions of samples to insure

that an accurate plate count can be achieved. It is not

appropriate to record plate counts that exceed 300

colonies on a plate, as the results are likely to be highly

inaccurate. Plates with this number of colonies are

likely to give a count that is lower than the true

count owing to two or more bacteria forming a single

colony and because colonies will tend to lie beneath

one another. Furthermore, some bacteria produce

bacteriocins which will inhibit the growth of other

organisms. The resultant plate counts are by no

means a measure of the total count of bacteria in a

water sample but merely indicate the number of or-

ganisms that are able to form colonies in the particular

medium used under specified growth conditions.

0006 Colony counts are not essential for assessing the

safety of potable water, but may be useful operation-

ally and may give an early indication of future

problems. The value of colony counts lies in the com-

parison of a number of counts from an individual

source taken over a period of time. When subjected

to trend analysis, any significant changes may indi-

cate problems. A sudden increase in the plate count at



C may indicate a pollution incident. Plate counts

at 22



C are subject to environmental and seasonal

influences. Plate counts are also particularly useful in

determining the efficiency of water treatment pro-

cesses such as filtration, coagulation, and chemical

disinfection.

Use of Automated Methods

0007 The development of automated procedures for the

microbiological testing of water samples has been

slow. To date, very little has been implemented.

Some automation of colony counts has begun and it

is not uncommon for laboratories to produce pour

plates using commercially available plate pourer/

stackers. Water is added to the Petri dish, a defined

volume of agar at the appropriate temperature is

added and, after mixing, the plates are cooled to

allow the agar to solidify. It is also possible to utilize

automatic colony counters to perform plate counts.

Colony counters composed of a solid-state video

camera coupled to sophisticated electronics and soft-

ware are often used. Such instrumentation can lead to

considerable time savings in a busy water microbiol-

ogy laboratory. New systems are being developed

which allow the enumeration of bacteria in a sample

without the need to grow them. Such systems employ

the use of viability markers such as fluorescein diace-

tate which is converted to a fluorescent product by

viable bacteria. This fluorescent product which is

held inside the bacterial cell wall allows sophisticated

instrumentation to enumerate the bacteria present on

a membrane surface.

Special Problems Associated with Viruses

0008All warm-blooded animals may harbor enteric viruses

and therefore have the potential for contaminating

water through defecation. In addition, other viruses

from other sites such as the respiratory tract may be

found in sewage and therefore may pass into source

waters. Fortunately, most viruses are extremely host-

specific and will infect only a small number of species.

(See Viruses.)

0009Human enteric viruses, which are now known to

occur frequently in raw water, were first isolated from

the environment over 50 years ago. This group in-

cludes viruses such as the polio virus and hepatitis A

virus. Whilst a direct association between the pres-

ence of virus in drinking water and human disease has

not been proved for all enteroviruses, their presence

in drinking water should be seen as a public health

hazard.

0010Viruses are small in size and may travel long dis-

tances through soil. Consequently they may be found

in sites where bacteria have been filtered out. For this

reason, the absence of indicator bacteria from water

does not mean that viruses are absent. It is therefore

appropriate to examine water for viruses in some

instances. This creates several problems. Because vir-

uses are intracellular parasites incapable of replica-

tion outside a host cell, they cannot be cultured on

artificial culture media as can most bacteria. Viruses

must be grown in tissue cultures, which are cells,

usually derived from animal or human tumor cells,

which can be grown in the laboratory. Because of

6118 WATER SUPPLIES/Microbiological Analysis