1 Introduction

1.1 Summarizer’s Note

This documented is intended to be a more digestible summary of the WHO Guidelines Vol. 3 for use by practitioners in the development and public health fields. Choices made in paraphrasing this content and in the omission of certain sections do not reflect the views of the WHO and CDC.

1.2 Document Outline

The structure of this document reflects key stages in the development of a surveillance program. It proceeds from planning (Chapter 2) to the collection of data from sanitary inspections and water quality testing (Chapters 3 and 4) to the analysis of said data (Chapter 5) and finally to the remedial actions which may be taken as a result of the surveillance program (Chapters 7 and 8).

1.3 Definitions and Performance Indicators

For the purposes of this guide, the term “communities” applies not only to villages and small private water supplies in rural areas but also to other centers of population within, or in close proximity to, urban centers.

If the performance of a community water-supply system is to be properly evaluated, a number of factors must be considered. Some countries that have developed national strategies for the surveillance and quality control of water supply systems have adopted quantitative service indicators for application at community, regional and national levels.
These usually include:

  • quality: the proportion of samples or supplies that comply with guideline values for drinking-water quality and minimum criteria for treatment and source protection
  • coverage: the percentage of the population that has a recognizable (usually public) water-supply system
  • quantity: the average volume of water used by consumers for domestic purposes (expressed as liters per capita per day)
  • continuity: the percentage of the time during which water IS available (daily, weekly or seasonally)
  • cost: the tariff paid by domestic consumers

Together, these five service indicators provide the basis for setting targets for community water supplies. They serve as a quantitative guide to the comparative efficiency of water-supply agencies and provide consumers with an objective measure of the quality of the overall service and thus the degree of public health protection afforded.

1.4 Health Implications

In most countries the principal risks to human health associated with the consumption of polluted water are microbiological in nature (although the importance of chemical contamination should not be underestimated).

The risk of acquiring a waterborne infection increases with the level of contamination by pathogenic microorganisms. However, the relationship is not necessarily a simple one and depends very much on factors such as infectious dose and host susceptibility. Drinking-water is only one vehicle for disease transmission. Some agents may be transmitted primarily from person to person and, for bacteria capable of multiplication in food, foodborne transmission may be more important than transmission by drinking-water.

However, pathogens of major concern like *Salmonella Typhi and Vibrio Cholera are frequently transmitted via contaminated drinking-water and, where this is the case, improvements in drinking-water quality may result in substantial reductions in disease prevalence.

1.4.1 Microbiological Aspects

Ideally, drinking-water should not contain any microorganisms known to be pathogenic-capable of causing disease-or any bacteria indicative of faecal pollution. To ensure that a drinking-water supply satisfies these guidelines, samples should be examined regularly. The detection of Escherichia coli provides definite evidence of fecal pollution (not necessarily from humans); in practice, the detection of thermotolerant (fecal) coliform bacteria is an acceptable alternative. (Need to update this last bit, thermotolerant / fecal coliforms now recognized as not that great of FIB.)

The WHO guideline for all water intended for drinking and in/entering the distribution system is that E. coli and thermotolerant coliforms must not be detectable in any 100-ml sample of water. However, it is important to note that the absence of E. coli and thermotolerant coliforms in a water samples DOES NOT indicate an absence of pathogens (protozoa in particular are more resistant to chlorine disinfection than bacteria). Rather, the quantification of bacteriological indicators can provide an important signal of process efficiency and the relative risk of different water supplies.

1.4.2 Disinfection

Terminal disinfection is essential for surface waters after treatment and for protected groundwater sources when E. coLi or thermotolerant (faecal) coliforms are detected. Chlorine in one form or another is the most commonly used disinfectant worldwide.

For terminal chlorination, there should be a free chlorine residual of at least 0.5 mg/liter after a minimum contact time of 30 minutes at a pH of less than 8.0, as for inactivation of enteric viruses. When chlorine is used as a disinfectant in a piped distribution system, it is desirable to maintain a free chlorine residual of 0.2-0.5 mg/liter throughout, to reduce the risk of microbial regrowth and the health risk of recontamination. In emergencies, e.g. in refugee camps, during outbreaks of potentially waterborne disease, or when fecal contamination of a water supply is detected, the concentration of free chlorine should be increased to greater than 0.5 mg/liter throughout the system.

High levels of turbidity can protect microorganisms from the effects of disinfection, stimulate the growth of bacteria, and give rise to a significant chlorine demand. Effective disinfection requires that turbidity is less than 5 NTU; ideally, median turbidity should be below 1 NTU.

Chlorine can be easily monitored and controlled as a drinking-water disinfectant, and regular, frequent monitoring is recommended wherever chlorination is practiced. Chlorine testing is discussed in section … The health-based guideline value for free chlorine in water supplied to the public is 5 mg/liter. However, concentrations that are detectable by consumers and may provoke rejection may be much lower than this (typically 0.6-1 mg/liter); an upper limit should therefore be established based on local experience.

1.4.3 Chemical Aspects

1.4.4 Physical Aspects

The chemical and physical quality of water may affect its acceptability to consumers. Turbidity, color, taste, and odor, whether of natural or other origin, affect consumer perceptions and behavior. In extreme cases, consumers may avoid aesthetically unacceptable but otherwise safe supplies in favor of more pleasant but less wholesome sources of drinking-water.

It is therefore wise to be aware of consumer perceptions and to take into account both health-related guidelines and aesthetic criteria when assessing drinking-water supplies.

  • Turbidity in excess of 5 NTU (5 JTU) may be noticeable and consequently objectionable to consumers.
  • Color in drinking-water may be due to the presence of organic matter such as humic substances, metals such as iron and manganese, or highly colored industrial wastes. Experience has shown that consumers may turn to alternative, perhaps unsafe, sources, when their water displays aesthetically displeasing levels of color, typically exceeding 15 TCU. Drinking-water should ideally be colorless.
  • Odour in water is due mainly to the presence of organic substances. Some odors are indicative of increased biological activity, while others may originate from industrial pollution. Sanitary surveys should include investigations of sources of odor when odor problems are identified.

A range of turbidities, credit: USGS.gov

The combined perception of substances detected by the senses of taste and smell is often called “taste”. “Taste” problems in drinking-water supplies are often the largest single cause of consumer complaints. Changes in the normal taste of a public water supply may signal changes in the quality of the raw water source or deficiencies in the treatment process. Water should be free of tastes and odors that would be objectionable to the majority of consumers.

1.4.5 Critical Parameters of Drinking Water Quality in Community Supplies

Since the main risks to human health associated with community water supplies are microbiological, it is possible use just a few types of water quality tests to judge the safety of supplies. This approach is sometimes referred to as “minimum monitoring” or “critical parameter testing”. It is much more effective to test for a narrow range of key parameters as frequently as possible (in conjunction with a sanitary inspection) than to conduct comprehensive but lengthy and largely irrelevant analyses less frequently.

The critical parameters of water quality are:

  • E. coli; thermotolerant (fecal) coliforms are accepted as suitable substitutes;
  • Chlorine residual (if chlorination is practiced).

These should be supplemented, where appropriate, by:

  • pH (if chlorination is practiced);
  • turbidity (if any treatment is effected).

A crucial advantage of these parameters is that they can be measured on site with relatively accessible testing equipment.

Analyses should also embrace the concept of acceptability: Volume 1 indicates that water supplied for drinking purposes should be inoffensive to consumers. Consumers may resort to a more palatable, but possibly unsafe, source if water is considered unacceptable; acceptability is therefore also considered a critical parameter. It may be assessed by observation (taste, color, odor, visible turbidity) and requires no laboratory determinations.

1.4.6 Other important analyses

When bringing a new water supply source online for the first time, a wider range of analyses is advised. For example, seasonal variations in turbidity and the chemical aggressiveness of the water need to be identified so that treatment plants can be designed for worst-case conditions and so that risks to pumping equipment can be planned for.

1.4.7 Water-washed diseases

The diseases most affected by the provision of adequate quantities of water for hygienic purposes are referred to as water-washed. They may be divided into the following three groups:

  • Diseases transmitted by the fecal-oral route, such as hepatitis A, bacillary dysentery, and many diarrheal diseases; these are transmitted by water and also by other means, such as food or hands. Improved hygiene therefore contributes to their control.
  • Infections of the skin and eyes, such as trachoma, skin infections, and fungal skin diseases. The prevalence of these diseases is related to poor hygiene.
  • Infections carried by lice or mites, such as scabies (mites), and louse-borne epidemic typhus (caused by Rickettsia prowazeki and transmitted largely by body lice). Good personal hygiene can assist in control.

1.5 Objectives of Surveillance and Quality Control

Surveillance

  • Surveillance is an investigative activity undertaken to identify and evaluate factors associated with drinking-water which could pose a risk to health.
  • Surveillance requires a systematic programme of surveys that combine analysis, sanitary inspection, and institutional and community aspects. Sanitary inspection should cover the whole of the water-supply system including sources, conduction lines, treatment plants, storage reservoirs, and distribution systems.
  • The surveillance agency is responsible for an independent (external) and periodic audit of all aspects of safety

Quality Control

  • Quality control is designed to ensure that water services meet agreed national standards and institutional targets.
  • Water quality control is the responsibility of the water supplier and involves the establishment of safeguards in the production and distribution of drinking-water as well as the routine testing of water quality to ensure compliance with national standards.
  • The water supplier is responsible at all times for regular quality control, and for monitoring and ensuring good operating practice.

1.6 Organizational Structure

1.7 Community Participation

1.8 Role of Surveillance in Improvement of Water Supplies

The results of a surveillance program can be used to improve water supplies through several mechanisms:

  • Establishing national priorities

When the commonest problems and shortcomings 1n water-supply systems have been identified, national strategies can be formulated for improvements and remedial measures, these might include changes in training (of managers, administrators, engineers, or field staff), rolling programmes for rehabilitation or improvement, or changes in funding strategies to target specific needs.

  • Establishing regional priorities

Regional offices of water-supply agencies can decide which communities to work 1n and which remedial activities are priorities, public health Criteria should be considered when priorities are set.

  • Establishing hygiene education

Not all of the problems revealed by surveillance are technical 1n nature, and not all are solved by supply and construction agencies, surveillance also looks at problems involving private supplies, water collection and transport, and household treatment and storage. The solutions to many of these problems are likely to require educational and promotional activities coordinated by the health agency.

  • Enforcement of standards

Many countries have laws and standards related to public water supply The information generated by surveillance can be used to assess compliance with standards by supply agencies Corrective act1on can be taken where necessary, but its feasibility must be considered, and enforcement of standards should be linked to strategies for progressive improvement.

  • Ensuring community operation and maintenance

Support should be provided by a designated authority to enable community members to be trained so that they are able to assume responsibility for the operation and maintenance of the1r water supplies.

2 Planning and Implementation of Surveillance

2.2 Planning

2.2.1 General Considerations

In addition to the main objectives of a surveillance and water quality control program listed in the previous chapter, some complementary objectives include:

  • provision of equipment and training;
  • determination of trends in the quality of the drinking-water supply service with time as shown by specific indicators
  • provision of information to public authorities for general public health protection purposes (i.e. information dissemination)
  • identification of sources of contamination
  • investigation of piped distribution networks
  • identification of remedial strategies;
  • assessment of the performance of water-treatment plants;
  • involvement of communities in the surveillance process.

Program targets bridge the gap between program objectives and the plan of work. Some early surveillance program targets might include:

  • preparation of a comprehensive water-supply inventory
  • development of preliminary standard methodologies (e.g. for analytical procedures, field work, and reporting)
  • establishment of regional laboratories capable of undertaking specified analyses
  • training of staff responsible for water sample analysis at regional and local levels
  • preliminary survey visits to a number of communities, and involving community members in surveys and briefings as a preparation for their role in community-based surveillance
  • implementation targets such as coverage (number of communities visited)
  • analysis of the data produced and dissemination of the findings to each community, to the local and regional authorities, to the water-supply and health agencies at regional and national levels, and to a national institution responsible for planning and coordination; community-based education in hygiene.

2.2.2 Strategies

Where it represents a new activity for health or environmental-protection agencies, the implementation of surveillance activities should begin at the pilot level, progress to regional level, and then expand to national level.

Any approach in which extension to the national level takes place too rapidly has a number of potential disadvantages. This is especially true where implementation at pilot and regional levels depends on a national authority. In these circumstances, extension to a national surveillance or quality-control program may make sudden and severe demands on the human and financial resources of this body.

The limited availability of resources makes it advisable to start surveillance with a basic program that develops in a planned manner. Activities in the early stages must generate enough useful data to demonstrate the value of surveillance. Thereafter, the objective should be to progress to more advanced surveillance as resources and conditions permit.

2.3 Implementation

Surveillance activities differ from place to place and should reflect local conditions. Factors influencing surveillance activities include:

  • the type and size of water-supply systems
  • the equipment, both existing and available
  • local employment practices, and the level of training of personnel
  • opportunities for community participation
  • geographical conditions (e.g. the accessibility of systems)
  • climatological conditions (which may hamper activities during certain seasons)
  • communication and transport infrastructure.

2.3.1 Inventories

It is important for a surveillance program to develop an inventory of the water supplies available to a community and what share of the population uses each supply. For example, a surveillance program of only piped water supplies is not advantageous if only a small portion of the community uses this source.

The inventory of supplies should draw on a combination of local community knowledge and field inspections. Where the initial inventory of supplies fails to account for the water consumption of a significant proportion of the population, it may be necessary to develop and implement a survey to determine the means by which water is supplied to the remainder of the population.

Another purpose served by the inventory is to estimate the workload on the surveillance agency and the cost of implementing a surveillance program.

2.3.2 Designing Forms

2.3.3 Training

The personnel responsible for data collection in the field need to be trained in a number of skills, including interviewing, working with communities, observation, sampling, and water-quality analysis. Adequate training in these areas will help ensure that surveillance findings are standardized throughout the programme and not subject to regional or local variations.

(Consider adding more and including training program diagram)

2.3.4 Undertaking Fieldwork

Staff responsible for field activities should ideally give local authorities advance notice of their visit, especially when a representative of the authority concerned must be present to provide access to parts of the supply system; staff should be accompanied by a representative of the supply agency whenever possible.

After on-site inspection and an analysis of the findings, problems or defects may be pointed out in the field to the local authorities or the representatives of the supply agency.

2.3.5 Establishing Routine Surveillance

The findings of the preliminary survey may have profound implications for subsequent surveillance activities; for example, surveillance should take due account of the most widely used method of supplying water for domestic purposes or the one that presents the greatest public health risk to the population.

2.4 Information Management

TBD

2.5 Support Structure

TBD

3 Surveys

3.1 Nature and Scope of Community Surveys

3.2 Sanitary Inspections

3.3 Sanitary Inspection Reports

3.3.1 Functions of Sanitary Inspection Report Forms

3.3.2 Design of Sanitary Inspection Report Forms

3.4 Carrying Out Sanitary Inspections

3.5 Timing and Frequency of Sanitary Inspections

3.5.1 New Sources

3.5.2 Routine Surveys of Existing Supplies

4 Water Sampling and Analysis

4.1 Sampling

4.1.1 Location of Sampling Points

One objective of surveillance is to assess the quality of the water supplied by the supply agency and of that at the point of use, so that samples of both should be taken. Any significant difference between the two has important implications for remedial strategies.

Samples must be taken from locations that are representative of the water source, treatment plant, storage facilities, distribution network, points at which water is delivered to the consumer, and points of use. In selecting sampling points, each locality should be considered individually; however, the following general criteria are usually applicable:

  • Sampling points should be selected such that the samples taken are representative of the different sources from which water is obtained by the public or enters the system.
  • These points should include those that yield samples representative of the conditions at the most unfavorable sources or places in the supply system, particularly points of possible contamination such as unprotected sources, loops, reservoirs, low-pressure zones, ends of the system, etc.
  • Sampling points should be uniformly distributed throughout a piped distribution system, taking population distribution into account; the number of sampling points should be proportional to the number of links or branches.
  • The points chosen should generally yield samples that are representative of the system as a whole and of its main components.
  • Sampling points should be located in such a way that water can be sampled from reserve tanks and reservoirs, etc.
  • In systems with more than one water source, the locations of the sampling points should take account of the number of inhabitants served by each source.
  • There should be at least one sampling point directly after the dean-water outlet from each treatment plant.

(This could be a spot to place more updated data on sampling such as from the da Luz and Kumpel, 2020 study)

When sampling a piped distribution network, it is important to note that samples are not necessarily representative of system-wide conditions but they may be able to capture the worst-case conditions if correctly sited.

Fixed sampling sites, while prone to missing important contamination events, are useful in holding suppliers accountable for improvements in water quality.

4.1.2 Sampling Frequency

need to figure out how to insert tables of suggested frequencies for piped and non-piped supplies

4.1.3 Sampling Methods for Microbiological Analysis

  • When collecting samples, ensure that outside contamination is not introduced
  • Glass bottles are recommended but Whirl-Pak ® bags are commonly used for collection
  • When sampling from a source where chlorine residual is expected, add sodium thiosulfate to inactivate the chlorine. The sodium thiosulfate should be added to sample bottles before they are sterilized.

A Whirl-Pak Bag with Sodium Thiosulfate Tablet,credit: hach.com

4.1.3.1 Sterilization of Bottles

  1. Loosely insert a stopper into the bottle, and tie a brown paper or aluminum foil cover to the neck of the bottle to prevent dust from entering.
  2. Then sterilize bottle in a hot-air oven for 1 hour at 160 or 170 °C for 40 minutes or in an autoclave at 121 °C for 20 minutes. If no other facilities are available, a portable sterilizer or pressure cooker can be used, but sterilization will then take 30-45 minutes.
  3. To prevent the stopper from getting stuck during sterilization, insert a strip of brown paper (75 X 10 mm) between the stopper and the neck of the bottle.

4.1.3.2 Sampling from a Tap or Pump Outlet

  1. Clean the tap: Remove from the tap any attachments that may cause splashing. Using a clean cloth, wipe the outlet to remove any dirt.
  2. Open the tap: Turn on the tap at maximum flow and let the water run for 1-2 minutes. Note: Some investigators do not continue to steps 3 and 4 but take the sample at this stage; in this case, the tap should not be adjusted or turned off, but left to run at maximum flow. The results obtained in this way will provide information on the quality of the water as consumed. If the procedure is continued to stages C and D, however, the results represent the quality of the water excluding contamination by the tap.
  3. Sterilize the tap: Sterilize the tap for a minute with the flame from a gas burner, cigarette lighter, or an ignited alcohol-soaked cotton-wool swab.
  4. Open the tap before sampling: Carefully turn on the tap and allow the water to flow for 1- 2 minutes at a medium flow rate. Do not adjust the flow after it has been set.
  5. Open the sterilized bottle: Take out a bottle and carefully unscrew the cap or pull out the stopper.
  6. Fill the bottle: While holding the cap and protective cover face downwards (to prevent entry of dust, which may contaminate the sample), immediately hold the bottle under the water jet, and fill. A small air space should be left to make shaking before analysis easier.
  7. Stopper or cap the bottle: Place the stopper in the bottle or screw on the cap and fix the brown paper protective cover in place with the string.

4.1.3.3 Sampling from a Watercourse or Reservoir

  1. Open the sterilized bottle as described in the previous section
  2. Holding the bottle by the lower part, submerge it to a depth of about 20 cm, with the mouth facing slightly upwards. If there is a current, the bottle mouth should face towards the current. If the technician must enter the watercourse to perform sampling, ensure that they stand downstream of where they sample.
  3. The bottle should then be capped or stoppered as described previously.

4.1.3.4 Sampling from Dug Wells or Similar Sources

4.1.4 Storage of Samples for Microbiological Analyses

  • The time between sample collection and analysis should, in general, not exceed 6 hours and 24 hrs is considered the maximum.
  • It is imperative that samples are kept in the dark and cooling is rapid.
  • Any chlorine residual present in the sample should be inactivated with sodium thiosulfate.

4.1.5 Sampling methods for Physicochemical Analyses

  • It is recommended that analyses for residual chlorine, pH, and turbidity are conducted immediately after sampling since these parameters will change during storage and transport.

4.2 Bacteriological Analysis

The main goal of the bacteriological analysis of water is to identify and enumerate organisms that indicate the presence of fecal contamination. The isolation of specific pathogens in water should only be undertaken by reference laboratories for the purpose of investigating and controlling outbreaks. Routine isolation of these pathogens is not practical.

4.2.1 Indicator Organisms

4.2.1.1 Escherichia coli

  • A member of the family Enterobacteriaceae
  • Possesses the enzymes \(\beta\)-galactosidase and \(\beta\)-glucuronidase (used for the identification of E. coli in enzyme substrate tests like the Colilert-18 method)
  • Grows at 44-45 C on complex media
  • Ferments lactose and mannitol with the production of acid and gas
  • Indole positive, Oxidase negative, Urea negative
  • Abundant in human and animal feces - concentrations can reach \(10^{9}\) per gram.

Link to more resources on E. coli / rational for why this is preferred FIB ?

4.2.1.2 Thermotolerant Coliforms

  • Coliform organisms that can ferment lactose at 44-45 C
  • Includes the genus Escherichia and some spp. of Klebsiella, Enterobacter, and Citrobacter
  • Thermotolerant coliforms (TTCs) can often live in environmental niches other than intestinal tracts and thus it is inappropriate to use the term “fecal coliforms”
  • If high counts of TTCs are found in the absence of detectable sanitary hazards, confirmatory tests specific to E. coli should be carried out.
  • Because TTC organisms are readily detected, they have an important secondary role as indicators of the efficiency of water-treatment processes in removing fecal bacteria.

4.2.1.3 Total Coliforms

  • "Coliform Organisms’ are gram-negative, rod shaped bacteria capable of growth in the presence of bile salts
  • Ferment lactose at 35-37 C with the production of acid, gas, and aldehyde within 24-48 hours.
  • Oxidase negative and display \(\beta\)-galactosidase activity (used for their identification in enzyme substrate tests like the Colilert-18 method).
  • “Coliforms” are a heterogenous group that includes some bacteria associated with feces and nutrient-rich waters, but also some bacteria that can multiply in relatively good-quality drinking water.
  • “Coliforms” are best used as indicators of water treatment efficiency - suspected fecal contamination should be confirmed with other more specific measures.

4.2.1.4 Fecal Streptococci

Not sure if this is still used

4.2.2 Analysis Method: Membrane Filtration

In the membrane-filtration (MF) method, a minimum volume of 10 ml of the sample (or dilution of the sample) is introduced aseptically into a sterile or properly disinfected filtration assembly containing a sterile membrane filter (nominal pore size 0.2 or 0.45 \(\mu\)m). A vacuum is applied and the sample is drawn through the membrane filter. All indicator organisms are retained on or within the filter, which is then transferred to a suitable selective culture medium in a Petri dish. Following a period of resuscitation, during which the bacteria become acclimatized to the new conditions, the Petri dish is transferred to an incubator at the appropriate selective temperature where it is incubated for a suitable time to allow the replication of the indicator organisms. Visually identifiable colonies are formed and counted, and the results are expressed in numbers of “colony forming units” (CFU) per 100 ml of original sample.

This technique is inappropriate for waters with a level of turbidity that would cause the filter to become blocked before an adequate volume of water had passed through. When it is necessary to process low sample volumes (less than 10 ml), an adequate volume of sterile diluent must be used to disperse the sample before filtration and ensure that it passes evenly across the entire surface of the membrane filter. Where the quality of the water is totally unknown, it may be advisable to test two or more volumes in order to ensure that the number of colonies on the membrane is in the optimal range for counting (20-80 colonies per membrane). This is often accomplished with a 10-fold dilution series.

4.2.3 Analysis Method: Most Probable Number (MPN) Method

The MPN method is based on an indirect assessment of microbial density in the water sample by reference to statistical tables to determine the most probable number of microorganisms present in the original sample. This method is essential for highly turbid samples that can’t be analyzed by membrane filtration.

The MPN method depends on the separate analysis of a number of volumes of the same sample. Each volume is mixed with culture medium and incubated. The concentration of microorganisms in the original sample can then be estimated from the pattern of positive results (the number of volumes showing growth in each series) by means of statistical tables that give the “most probable number” per 100 ml of the original sample.

In the past, this method was very time consuming as it involved the measurement of several different sample volumes into separate glass tubes for each sample.

Now, with the use of the IDEXX Quantitray and Colilert-18 medium, the procedure is much simpler, although the costs are higher than for the membrane filtration method.

4.2.4 Presence Absence Tests

Presence-absence tests are not recommended for use in the analysis of surface waters, untreated small-community supplies, or larger water supplies that may experience occasional operational and maintenance difficulties.

4.2.5 Choice of Methods

Look into updating pros and cons table to accommodate use of IDEXX method

4.2.6 Minimizing the Cost of Analysis

Unless there is a legal requirement to test, in situations where fecal contamination very likely (downstream of a sewage discharge) or unlikely (in a distribution system with free chlorine residual greater than 0.5 mg/ liter), microbiological analysis may be omitted to reduce costs.

4.2.7 Laboratory-based versus On-site Testing

5 Data Analysis and Interpretation

6 Technical Interventions

7 Hygiene Education