Hygiene and Environmental Health Module: 16.  Sanitary Survey of Drinking Water

Study Session 16  Sanitary Survey of Drinking Water

Introduction

Diseases related to contamination of drinking water constitute a major burden on human health. The great majority of water-related health problems are the result of microbial (bacteriological, viral, protozoan or other biological) contamination. Sanitary surveying of drinking water is an important tool for reducing the risks of water contamination and waterborne illness. In Study Session 15 you learned that undertaking a sanitary survey is an important part of the process to develop a new water source. Sanitary surveys are also essential for monitoring the condition of existing water sources to ensure they continue to be safe to use.

Learning Outcomes for Study Session 16

When you have studied this session, you should be able to:

16.1  Define and use correctly all of the key words printed in bold. (SAQ 16.1)

16.2  Describe the purpose and benefits of a sanitary survey. (SAQ 16.2)

16.3  Describe the purpose and benefits of water quality analysis. (SAQs 16.3 and 16.4)

16.4  Explain the methods of conducting a sanitary survey at different water sources. (SAQ 16.5)

16.1  Rationale for a sanitary survey

In Study Session 15 you learned that a sanitary survey is an evaluation of the physical environment to identify possible health hazards and sources of environmental contamination. The survey should include an inspection of the entire water system, including the water source, facilities, equipment, operation and maintenance. It can be a complex technical task if carried out at a detailed level and may require expert help but you can conduct an onsite survey of the key elements, which are the water source itself, sources of contaminants and water handling by household members. There are many different aspects to a sanitary survey and different questions to be answered, so having a checklist of the necessary items is a useful aid. Some example checklists are included later in this session.

There are several reasons for conducting sanitary surveys of drinking water. Sanitary surveys are a comprehensive inspection of the entire water delivery system from the source to the mouth and are, therefore, the best means of identifying potential problems and changes in the quality of drinking water. They play a fundamental role in ensuring that consistent and safe drinking water supply is provided to the community by identifying and correcting any deficiencies in the system, and helping to identify public health risks related to drinking water.

The benefits of a sanitary survey, therefore, are that they can:

• Assure the long-term quality and safety of drinking water.
• Help to protect public health.
• Reduce the risk of waterborne disease outbreaks.
• Help source protection.

After conducting a sanitary survey you will be able to describe the extent of problems and consider possible solutions, which will vary depending on the circumstances. You can discuss these with the community leaders, religious leaders and local administrators, and perhaps find a rapid solution, if it is controllable by you. If the problems are more difficult to handle, you can report to the experts who are working at the district level.

A sanitary survey or inspection is a relatively simple technique that depends on gathering information, principally by observation and also by making enquiries. A more detailed assessment of water quality would require chemical and microbiological analysis, which would need specialised equipment and qualified staff, and would be more expensive than a sanitary survey. Some analytical equipment is portable and can be taken to the site but other tests can only be done in a laboratory. The recommended tools for field use are a portable pH meter with digital readout, a hand-held colorimeter, portable spectrophotometer and residual chlorine test kit.

16.2  Elements of a sanitary survey

One of the most important functions of the onsite sanitary survey is to determine whether the existing facilities are adequate to meet the needs of the users at all times. This is one of several elements that are considered essential in the proper conduct of a thorough sanitary survey. The two key elements that you should focus on are the water source (its physical components, protection and condition of any associated structures) and the use of water at home.

16.2.1  Water source (components, protection and condition)

As you know, the water supply source is the beginning of the drinking water system. Preventing source water contamination is the most effective means of preventing contaminants from reaching consumers. Source water protection also helps you to ensure the least expensive method is used for treatment of water. Hence, a sanitary survey should be designed to assess the control of contaminants and determine the reliability, quality, quantity and vulnerability of the source of water.

During a sanitary survey, you need to consider the terrain (the slope of the land), soil types, land cover, rainfall and runoff, and animals, which can all affect the water quality. In particular the potential sources of contamination by pathogens need to be assessed.

In addition to contamination by pathogens from human body waste, there are many other human activities that can affect water quality. Runoff from barnyards and other areas where animals are kept will contain animal wastes and can cause significant problems. Farming activities can also lead to contamination from pesticides that may percolate into groundwater or wash off from fields into surface waters. Construction activities can result in large amounts of sediment being washed into rivers and streams.

Flooding is a natural event that may also be a source of contamination to sources of water supply. Surface runoff, which is a major contributor to flooding, can carry dirt, oil, pesticides, fertilisers and other contaminants that might be washed off from surrounding land.

16.2.2  The use of water at home

As you know, water is said to be safe to drink when it is free from pathogens, physical contaminants and chemical contaminants. This needs to apply right up to the point when water goes in the mouth. Identifying and assessing the potential risks associated with the collection and use of water is therefore a very important part of the survey (Figures 16.1 and 16.2). You need to ask users, or observe their practice, on:

• How they collect the water and the types of vessel they use (e.g. whether jerrycan, buckets or pots).
• How the vessels are handled and stored when not in use.
• Whether the vessels are used for purposes other than water collection that may contaminate them.
• Whether users know how to collect safe water and keep it safe.
• Whether the water is treated or disinfected after collection and assess the hygiene practices of users, especially young children.

Figure 16.1  Collecting water in jerrycans and traditional pots. (Photo: Richard Adam)		Figure 16.2  Water storage at home. (Photo: Nancy Platt)

16.3  Vulnerability assessment at a water source

A vulnerability assessment is used to determine the likelihood that potential contaminant sources in the drinking water protection area will degrade the source water quality. A vulnerability determination will include consideration of several factors including hydrological sensitivity, the source of contaminants, how these sources can be managed, and the condition of any water source protection.

Hydrological sensitivity means assessing how sensitive a water source is to contamination. Higher sensitivity ratings apply if geological conditions allow contamination to move quickly from its place of origin through the rocks and soil to water sources. Lower ratings apply when contamination moves more slowly.

Another factor is vegetation and surrounding land use. If the land around a water source has no vegetation it is more susceptible to contamination than a water source surrounded by land with thick vegetation. This is because plants and trees can act as a physical and biological barrier to pollutants.

You also need to look at the condition of source water structures. For example, at a well you need to check the well casing, joints, delivery structures and equipment to move water from the well and assess their integrity. ‘Integrity’ means the quality of design, construction, maintenance and state of repair of the structure.

Factors affecting vulnerability to contamination include:

• Drinking water wells located close to potential sources of contamination have more risk than wells located further away.
• Whether the potential source of contamination is from a single identifiable point which would be easier to manage but could have greater potential for major contamination than diffuse contamination spread over a wider area.

16.4  Source water quantity

The quantity of water for users is also an important part of a sanitary survey. An adequate quantity of source water should be available to meet the community’s needs. The quantity must be sufficient to meet the anticipated demand of the community. The location of source water supply facilities is also an important factor in determining the ability of the water system to meet the community’s needs at all times. The source should be within 1 km or a 30-minute round trip.

16.5  Sanitary survey of wells

Wells should have a well casing (a liner pipe or tube or stone wall), protective devices such as good fences, and warning signs to discourage human and animal activities that might disturb the well area. Figure 16.3 shows what you should be looking for when you are doing a sanitary survey of a well, and Box 16.1 has a list of questions to be asked. The numbers in the diagram demonstrate particular points and correspond to the questions in the checklist. Answering ‘yes’ to any of the questions would be a cause for concern.

Note that the minimum safe distance (MSD) between the well and potential sources of pollution will vary depending on the local conditions, particularly the soil type, geology, hydraulic gradient and slope of the land. It should never be less than 15 metres but 30–50 metres is recommended.

In addition to the observations of the physical condition of the well and its surroundings, you should also find out and make a note of the maintenance programme for the well, for example, the frequency of cleaning and disinfection.

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Figure 16.3 Sanitary inspection of a well with handpump. The numbers refer to the questions in Box 16.1. Note: MSD means ‘minimum safe distance’. MSD will vary depending on local conditions but should not normally be less than 15 m. (Source: World Health Organization, 1997, Guidelines for drinking water quality, Volume 3)

16.6  Sanitary survey of springs

When a spring is chosen for a water supply, the sanitary survey should determine that the water quality is acceptable, the quantity of water available is adequate to meet the needs of the community and the spring is protected from contamination. The quantity of water available from a spring can vary significantly due to changes in groundwater storage.

Like wells, springs should have protective devices such as good fences and warning signs to discourage human and animal activities that might disturb the spring area. The spring box or storage tank and cover need to be watertight to prevent undesirable water from entering. Since most springs never stop producing water, an overflow is needed to ensure that water pressure does not build up and damage the spring box. The end of the overflow drain should have a screen to prevent the entrance of animals. Springs should have a diversion ditch located at the uphill end of the site which keeps rainwater from flowing over the spring area. A good impervious barrier, such as clay or a plastic liner, can help ensure high quality water by preventing potential contaminants from entering the collection facilities. Figure 16.4 shows what you should be looking for when you are doing a sanitary survey of a spring and Box 16.2 has a list of questions to be asked. The numbers in the diagram demonstrate particular points and correspond to the questions in the checklist.

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Figure 16.4  Sanitary inspection of a protected spring. The numbers refer to the questions in Box 16.2. (Source: as Figure 16.3)

16.7  Sanitary survey of rainwater collection and storage

As you learned in Study Session 15, rainwater harvesting is applicable for areas that have a shortage of other water sources. The roof from which rain is collected should be free from contaminants. There also needs to be a clean and well-constructed tank with no cracks in the walls and a properly covered inspection hole. Figure 16.5 shows what you should be looking for when you are doing a sanitary survey of rainwater collection and Box 16.3 has a list of questions to be asked. As before the numbers in the diagram demonstrate particular points and correspond to the checklist of questions. Any ‘yes’ answers would be a cause for concern.

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Figure 16.5  Rainwater collection and storage. The numbers refer to the questions in Box 16.3. (Source: as Figure 16.3)

16.8  Water quality assessment

As you know, water can be polluted by chemical or biological contaminants and the water may be harmful to humans when consumed. There are many analytical methods used to test for the presence and concentration of possible pollutants. You are not expected to carry out microbiological and chemical tests of drinking water but it will help you if you understand the principles.

If at all possible, drinking water should not contain any pathogenic microorganisms. It would be very difficult and time-consuming to test for all the possible pathogens. The source of the pathogens is usually human faeces; therefore, tests have been devised that detect the presence of faecal contamination. If faecal contamination is found, this indicates that pathogenic organisms may be present.

The most widely used tests for faecal contamination are total coliforms, faecal coliforms and Escherichia coli (E.coli). Coliforms are a group of bacteria found in human and animal faeces and also in soils and some other natural environments. ‘Total coliforms’ includes all bacteria in this group. The presence of ‘total coliforms’ indicates contamination of some sort but, because of their relatively wide distribution, cannot be used to confirm if the contamination is from faeces.

Faecal coliforms are a sub-set of total coliforms and, as the name suggests, are typically found in faeces. However, even this group includes some species that are not necessarily faecal in origin. E.coli is a type of faecal coliform bacterium that is found only in faeces of humans and other warm-blooded animals. If E.coli is present in a water sample, this indicates faecal pollution and the possible presence of pathogenic types that often occur in the intestines as well; the absence of E.coli from a sample shows that the chances of faecal contamination of the water, and therefore of pathogens being present, are negligible. Thus the presence or absence of E.coli in a water sample provides an important indicator of pollution and public health. However, it is important to realise that E.coli is only an indicator and its absence cannot give complete assurance that water is safe. Some pathogens such as Giardia, Entamoeba histolytica and some viruses are more resistant to disinfection than E.coli; therefore, the absence of E.coli will not necessarily mean that water is totally free from other organisms.

Although the great majority of health-related water quality problems are the result of bacteriological contamination, chemical contamination of water sources can also cause serious health problems. For example, the presence of nitrate and nitrite in water may result from the excessive application of fertilisers or from seepage of wastewater into surface water and groundwater. Fluorosis is a common problem in children living in the Rift Valley region of Ethiopia caused by exposure to high levels of naturally occurring fluoride in the water which can lead to mottling of children’s teeth (Figure 16.6), skeletal fluorosis and crippling.

Figure 16.6  Fluorosis causes mottling of children’s teeth (Photo: Basiro Davey)

Some health effects may occur as a result of specific chemical deficiencies in the diet, of which water forms a part, for example, goitre caused by iodine deficiency and dental caries resulting from low fluoride intake.

Turbidity, colour, taste and odour (smell), whether of natural or other origin, affect people’s perceptions of water. As you know water should be free of tastes and odours that would be unpleasant to the majority of people. In extreme cases, people may avoid water that does not look or taste good – even if it is otherwise safe – in favour of more pleasant looking and tasting water that may actually be contaminated. Colour in drinking water occurs due to the presence of organic matter and metals such as iron and manganese. Odour in water is due mainly to the presence of organic substances. Taste is the combined perception of substances detected by the senses of taste and smell. Changes in the normal taste of a municipal water supply can be important as they may signal changes in the quality of the raw water source or deficiencies in the treatment process. Onsite testing is essential for the determination of turbidity and residual chlorine, which change rapidly during transport and storage.

Summary of Study Session 16

In Study Session 16, you have learned that:

1. Sanitary surveys play a major role in prevention and correction of water system deficiencies.
2. Sanitary surveys begin at the source of the water. Preventing source water contamination is the most effective means of preventing contaminants from reaching consumers.
3. Source water quality, quantity, location of water source and condition of the water source facilities are the key elements of a sanitary survey.
4. Sanitary surveys also include assessment of water use in the home and ensuring that household practices do not allow recontamination.
5. Wells, springs and rainwater cisterns are important sources of water to which you need to pay attention when you are doing sanitary surveys.
6. Faecal coliform bacteria and E.coli are used to test for the presence of faecal contamination and to indicate the likelihood of the presence of pathogenic organisms in drinking water.

Self-Assessment Questions (SAQs) for Study Session 16

Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering the following questions. Write your answers in your Study Diary and discuss them with your Tutor at the next Study Support Meeting. You can check your answers with the Notes on the Self-Assessment Questions at the end of this Module.