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.
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)
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:
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.
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.
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.
What pathogens might be a problem for water quality and what are the sources of those pathogens?
The pathogens are bacteria, protozoa, viruses and helminths. The primary source is human waste which gets into the water because of open defecation, discharge of sewage to water bodies, poorly sited latrines, etc.
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.
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:
|Figure 16.1 Collecting water in jerrycans and traditional pots. (Photo: Richard Adam)||Figure 16.2 Water storage at home. (Photo: Nancy Platt)|
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:
Can you think of an example of a possible source of contamination of a water well?
Contamination could be caused by a pit latrine or other waste disposal pit if it is sited at a higher level than the well and/or is too close. The wastewater from the pit could slowly seep through the rocks into the groundwater.
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.
What is the recommended minimum volume of water needed per person per day?
The minimum volume is 20 litres per person per day.
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.
Name of Health Post ------------
Village name and location of well/handpump
Questions to be asked during survey:
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.
Name of Health Post ------------
Village name ------------
Questions to be asked during survey:
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.
Name of Health Post ------------
Village name ------------
Questions to be asked during survey:
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.
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.
In Study Session 16, you have learned that:
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.
Which of the following statements is false? In each case explain why it is false.
A E.coli is a type of virus found in faeces.
B Faecal coliforms are typically found in human and animal faeces.
C The presence of E.coli in a water sample means the water is safe to drink.
D The absence of E.coli in a water sample means the water is safe to drink.
A is false. E.coli is a type of bacteria, not a type of virus.
B is true. Faecal coliforms are found in faeces.
C is false. If a water sample is positive for E.coli this indicates faecal contamination, which means it is likely that pathogens are present in the water.
D is also false. The absence of E.coli indicates the water is not contaminated with bacteria of faecal origin but it does not mean it is safe to drink because the water may contain other pathogens.
In a village there is a protected dug well. The water is treated frequently by chlorine and contamination is avoided. However, you hear that there are several cases of diarrhoea in children. Where would you suspect the water could possibly be recontaminated and what would you do?
You would have to do a sanitary survey to check the possible reasons for the childhood diarrhoea. This would include checking how the water is handled because it may be exposed to recontamination after it is collected from the protected well. Pots and buckets used for collection and storage should be checked to see if they are left open or not. If they are open, and people dip smaller containers into them, there is greater chance of recontamination. A jerrycan is preferable because it has a small opening that cannot be used for dipping. The cleanliness of the containers may be poor because of improper washing or the container may be used to collect both unclean and clean water. You may need to educate the families concerned about good hygiene and the proper handling of water.
Suppose you have a joint plan with environmental health experts to assess the quality of water from a well. What tests would you do?
Together with the environmental health experts you would conduct tests to measure the colour, taste and odour. You may test pH and for certain chemicals such as nitrate, fluoride and chloride, using portable water field test kits where available. You might also test turbidity (suspended solids). Water analysis would include microbiological tests as well as chemical tests. To do this a water sample would need to be taken and sent to a central laboratory for E.coli assessment and other microbiological tests.
The people in Agita village have two possible water sources available to them – a protected well and a river. Water quality surveys were undertaken by you and environmental health experts. The results indicate that the river water is highly contaminated with pathogenic microorganisms, but it has a good taste. The well water is tasteless but is not contaminated with pathogenic microorganisms. How would you explain to the villagers that they should use water from the well?
You should tell the villagers that the river water is contaminated with pathogens and will cause waterborne diseases. Without any treatment, the surface water should not be used for drinking and domestic purposes. The water from the well may not taste so nice but it is safer to drink and use for domestic purposes. You will need to advise them that the tests reveal more about water quality than taste does.
You are about to set off from your Health Post for a neighbouring village to conduct a sanitary survey of a protected spring. What would you take with you? Name four things you will be looking for during your survey.
You would need to take an appropriate checklist of questions to ensure that you survey thoroughly and don’t forget anything. You will also need a notebook and pen or pencil to record all the information you collect. Important things to look for include the location of any latrines or other possible sources of contamination relative to the spring, a sound fence, the condition of the concrete/stone box that protects the spring, the presence of a diversion ditch and any other defect in its construction that could affect the water quality. Your answer could include any four of these or related issues.