Every public drinking water source should be protected from possible contamination. In this study session, you will learn about different sources of water, the basic techniques of developing small-scale drinking water schemes (i.e. springs, hand-dug wells, rainwater harvesting and surface water). You will also learn how to identify water sources that need protection and how they can be protected from potential contaminants through community mobilisation, regular inspection, proper maintenance, hygiene promotion and periodic treatment of water to prevent waterborne diseases from affecting the community.
When you have studied this session, you should be able to:
15.1 Define and use correctly all of the key words printed in bold. (SAQ 15.1)
15.2 List the different sources of drinking water. (SAQ 15.2)
15.3 Describe the main activities when planning and developing water source protection. (SAQ 15.2)
15.4 Describe the methods of preventing contamination of well and spring water. (SAQs 15.3 and 15.4)
The sources of drinking water that are practicable for public and domestic purposes are classified as:
Rainwater can be used for domestic purposes in areas where there are no alternative sources of water such as springs, rivers and lakes, or where these sources of water are contaminated. The term rainwater harvesting is sometimes used. It simply means collecting, or harvesting, rainwater as it runs off from hard surfaces such as rooftops and storing it in a tank or cistern (Figure 15.1).
The main advantage of rainwater is that it is free. It is fairly reliable though obviously dependent on the amount of rain that falls. It does not usually require pumps or pipes and is available at the doorstep. Using rainwater can reduce the burden on women and children who typically are the water carriers in Ethiopia and walk long distances to fetch inadequate supplies.
Surface water supplies are taken from rivers, lakes or ponds. Surface water can provide a consistent and manageable source of water. However, it is subject to greater risk of contamination than groundwater and therefore usually requires treatment. Contamination is most likely to be with microbiological pathogens from human and animal excreta. There is also the possibility of accidental or deliberate pollution by industries or the agricultural community.
What are the likely sources of contamination in the river in Figure 15.2?
Excreta from the cattle will be washed into the river water. Their hooves have disturbed the ground so soil is also likely to be washed in. The road passing over the bridge in the background could be a source of pollution from cars and lorries.
Groundwater is water found beneath the ground surface held in the spaces within porous soil and rock. Groundwater can be obtained from springs, boreholes or wells. A borehole is a particular type of well with a narrow shaft. Usually a drilling rig is needed to drill (bore) the hole into the rock.
The depth that water is taken from and the types of rock it has passed through are important factors that affect the quality of the groundwater. Groundwater, particularly from deep sources, may provide water of good microbiological quality. This is because bacteria, protozoa, viruses and helminths are filtered from the water as it passes through the layers of soil and rock into the groundwater. Groundwater sources are therefore preferable to surface water sources. However, groundwater can contain chemical contaminants, such as arsenic, fluorides and nitrates.
Permeable rocks have tiny spaces between the solid rock particles that allow water and other fluids to pass through and be held within the rock structure. Impermeable rocks do not have these spaces and water cannot pass through them.
A spring occurs at the point where the boundary between a permeable layer of underground rock and an impermeable layer reaches the ground surface. Rainwater percolates (trickles down) through the soil into permeable layers of subsoil or underground rock. The downward percolation will be stopped if this layer sits on top of an impermeable layer and the water can go no further. Depending on the slope of the layers, the water will run along the top of the impermeable layer to a point where it reaches the surface and emerges as a spring (see Figure 15.3). A spring may vary in volume and contamination levels according to the amount of rainfall.
Springs are likely to be polluted by direct contamination through the topsoil unless the surrounding land area is protected. A spring supply issuing from a deep, water-bearing layer, rather than a permeable layer near the surface, can produce both a consistent volume and a better quality supply. Whether the spring originates from shallow or deep rock layers, animals should be excluded from the surrounding area by a stock-proof fence, and any water running off the land after rain should be diverted to a suitable ditch away from the spring.
The practice of obtaining water from wells is common and well water is an important source of supply in many developing countries like Ethiopia. A well should be located uphill from any possible sources of pollution. Wells are classified based on the depths of the water-bearing layers as follows:
As you learned in Study Session 13, nearly 70% of the rural population of Ethiopia get their water from unimproved sources. There is, therefore, a widespread need to develop new sources of water and to ensure they are adequately protected. Several issues need to be taken into consideration when planning the protection and development of water sources.
Water source protection should be based on needs identified by the community themselves. The community should identify its own water and sanitation needs through a process of internal discussion and external negotiation. The internal discussion would involve you, other health experts, community leaders and other members of the community. Local people have local knowledge and it is important to draw on this knowledge when planning new developments. The external negotiations may involve local government offices, NGOs and other partners who can assist with the assessment of the communities’ needs with information and technical guidance.
All potential water sources should be considered and checked. Issues to consider are the sources of possible contaminants, the amount of water available to users annually and the consistency of the supply. Other important issues are social acceptance, cost effectiveness and community health. All potential water sources need to be assessed in order to identify the best solution.
For instance, whenever rivers and streams are considered for use and development, the communities immediately upstream and downstream should be consulted and involved in the decision-making process prior to implementation. This is because both quality and quantity of surface water can be affected by the activities of the people living upstream (toward the source of the stream or river). If the upstream users abstract large volumes or pollute the water, this will have a damaging effect on the downstream users (Figure 15.4). All communities have an interest in having good quality and adequate quantities of water; therefore, it is important that proposed surface water developments should be discussed with and agreed by both the upstream and downstream communities.
Whenever a new protected water source is proposed it should have the capability of supplying at least 20 litres of water per person per day to the target population. The protected water source should provide sufficient quantities of water to meet essential health-related household and personal needs, including drinking, cooking, personal hygiene, clothes washing and cleaning for all community members.
Before any new water source protection is developed or maintenance is planned on an existing source, it is important to conduct a sanitary survey. A sanitary survey is an evaluation of the physical environment to identify possible health hazards and sources of environmental contamination. It will reveal the potential risks to the health of people that may arise from the proposed water source. The risks may be negligible or they may need to be controlled with specific correction activities. This sanitary survey will be part of the baseline information for the water source development and should include the nature of the water-bearing layer, the hydraulic gradient (i.e. the variations in underground water pressure that affect the natural flow of water), topography, vegetation, potential sources of contamination, and the adequacy of the yield particularly for dry seasons. (You will learn more about sanitary surveys in Study Session 16.)
Before developing any water protection, the health benefits of an improved water supply and sanitation need to be accepted by the local community. You can provide hygiene education for the people in order to promote their behavioural change.
What good hygiene practices would you encourage so that the local community get the full benefit of an improved water supply?
The most important aspects of good hygiene education would be:
Water and sanitation activities should be integrated with community health developments if it is possible. Individual and community health are the major beneficiaries of improved water supplies and sanitation.
Water quality should be a primary concern in all water projects. Water quality is a description of the chemical, physical and biological characteristics of water, usually with respect to its suitability for drinking. The quality of drinking water must be uppermost in the planning and implementation of water and sanitation activities. Water source development projects should draw water from the best available sources. Water quality assessment is discussed in more detail in Study Session 16.
There are several different ways of constructing a well in order to access groundwater sources. These include dug wells, bored wells (also known as boreholes), and driven and jetted wells.
A dug well is usually excavated by hand, but may be dug by mechanical equipment. They are usually 90–180 cm in diameter and 4.5–10.5 m deep, depending on where the water-bearing layer or groundwater is encountered. Wider and deeper dug wells are less common. Dug wells have a relatively large diameter and therefore have large storage capacity, but the water level will be lower at times of drought and the well may go dry. On the other hand, during heavy rain, dug wells are susceptible to contamination by pathogens which may be deposited on the surface or naturally present in the soil and are washed in to the well, particularly if it is improperly constructed. Handpumps placed over the well need to be built so the surrounding ground is covered and protected (Figure 15.5). Any pipework associated with pumps that enters the well needs to have watertight connections so there can be no contamination from surrounding soil.
Bored wells or boreholes are constructed with a hand- or machine-driven auger and tend to be used in relatively soft soils and rocks. An auger is a device with a rotating blade that is used to drill holes and draw out the loosened rock and soil. Bored wells vary in diameter from 5–75 cm and in depth from 7.5–18 m. A lining, known as a casing, of concrete, metal, or plastic pipe is necessary to line the hole and prevent the soil and rock from caving into the well. Bored wells have characteristics similar to dug wells in that they have small yields, may be easily polluted, and are affected by droughts.
These types of well consist of a metal pipe with a screen attached at the bottom end. A well screen is a device that allows water to pass in to the pipe but keeps out soil particles. The pipe is driven or jetted into a water-bearing rock layer found at a comparatively shallow depth. For a driven well, the end of the pipe is shaped into a point and it is hammered into the ground. The jetted well is constructed by directing a high velocity stream of water through the bottom of the pipe, thereby loosening and flushing out the soil which is forced back up to the surface as the pipe is lowered. Driven wells are commonly 2.5–5 cm in diameter and less than 15 m in depth. Jetted wells may be 5–30 cm in diameter and up to 30 m deep. Larger and deeper jetted wells can be constructed. Following development, the well should be tested to determine the dependable well yield (I.e. the volume of water reliably produced). The well is then disinfected and the project completed.
Before and during water source development, care should be taken to minimise possible risks. The well should be located on a higher level than possible sources of contaminants such as latrines and cesspits (a pit for collection of waste matter and water especially sewage). This is because the liquid from the pit may seep into the surrounding ground and into the groundwater. If the latrine is higher up a slope than the well then the contaminated groundwater is likely to flow downwards and into the well. The natural flow of the groundwater (the hydraulic gradient) should be away from the well and towards the sources of contaminants, and not the other way round. In normal soils, the minimum distance between the well and the source of contaminants should never be less than 15 metres and a distance of 30–50 m is recommended. However for limestone and some other soil formations this distance needs to be greater because groundwater can pass very easily through some rocks and soils.
The inside wall of the well should be made waterproof by constructing a well casing. As noted above, in small diameter bored wells the casing can be a pipe, but in larger wells the casing needs to be constructed by cementing from the top of the well down to a minimum depth of 3 metres. The casing of the well should also be extended for a minimum of 60 cm above the surrounding ground level to prevent the entrance of surface runoff. A concrete cover should be fitted over the casing to prevent dust, insects, small animals and any other contaminants from falling in (Figure 15.6).
A pump should be installed, but if a pump is not available then a sanitary bucket and rope system may be used. The immediate area of the well should preferably be fenced to keep animals away (see Figure 15.5). The area surrounding the well should be graded off (i.e. should slope away from the well) in order to prevent the flow of storm water into the well.
The causes of bacterial contamination in a well are usually due to:
At the time when a new well is constructed or repairs are made to a well, pump or piping, contamination from the work is possible. Therefore, it is important that the well, pump, piping and associated structures should be regularly disinfected using chlorine solution.
There are different methods which help to identify a possible source of groundwater contamination. One method is sodium or potassium fluorescein. This is a brightly-coloured, fluorescent, water-soluble dye and can be used as a tracer when a sewage disposal system is suspected of contaminating groundwater. A solution flushed into the disposal system or suspected source may appear in the well water within 12–24 hours. It can be detected by sight, taste or analysis.
There may not be many opportunities to develop new spring sources but, if the opportunity does arise, there are certain procedures to follow to ensure the spring water is protected and safe to drink. You would be working with others if a new spring source was to be developed but the same principles will apply to existing spring sources because the protection needs to continue to work into the future.
Before using a spring a thorough sanitary survey needs to be carried out at the site to assess the quantity and quality of water, and the possible contamination. (Sanitary surveys are described in Study Session 16.) If the results of the sanitary survey are satisfactory, the eye of the spring (the point where the water emerges from the ground) should be located by digging out the area around the spring down to the impermeable layer.
Different types of spring protection can be constructed but in general they are as follows:
Springs should be protected from flooding and surface water pollution by constructing a deep diversion ditch above and around the spring. The ditch should be constructed so it collects surface water running towards the spring and carries, or diverts, it away. It needs to be deep enough to carry all surface water away, even in a heavy rainstorm. The surrounding area should be fenced to protect it from animals (see Figure 15.7).
A lot of care must be taken to ensure rainwater that is used for water supply is not contaminated by improper methods of storage or by bird droppings and leaves from the roof the water is collected from. Rainwater may be also be contaminated by pollutants in the air, dust, dirt, paint and other material on the roof or in roofing materials. All of these contaminants can be washed into the storage tank or cistern.
To protect the water, various precautions are needed. The tank must be completely covered and well maintained. The roof and gutters should be cleaned regularly, especially before the start of the wet season. It may be necessary to divert the first rainwater away from the tank so the dust and dirt is washed away. Leaves and other larger debris can be prevented from entering the tank by placing a mesh screen between the guttering and the pipe that leads to the tank; the mesh screen will need to be cleaned regularly.
All surface water sources are subject to continuous or intermittent pollution and must be treated to make them safe to drink. One never knows when the organisms causing diseases such as typhoid fever, gastroenteritis, giardiasis or infectious hepatitis A will contaminate surface water sources. The extent of the treatment required will depend on the results of a sanitary survey made by an experienced professional, including physical, chemical and microbiological analyses. Protecting surface water from pollution is difficult because, as noted earlier, the activities of upstream users of the river water will affect the quality of the water for downstream users and the land use in the surrounding area will also have an impact. Surface waters are, by definition, unprotected sources.
In Study Session 15, 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 these 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.
Match the following phrases with the corresponding words below.
Using the following two lists, match each numbered item with the correct letter.
Rivers and lakes
Freshwater supply beneath the Earth’s surface
Underground water-bearing rock layer
Water trickling down through soil
A community leader in a village comes to your office claiming the villagers use water from an unprotected source. He asks if you can help in the development of a new water source. What steps need to be taken to investigate if a new water source was possible for this village?
A plan for the new water source would need to be prepared. This would involve the community, the community leaders and the local administration. The following steps would be needed:
Suppose inhabitants of a village obtain water from a spring. What advice do you give to the users about the prevention of contaminants?
The users of the spring should be advised to:
Look at Figure 15.8 which shows a handpump over a well. What are the potential sources of contamination of the water in this well? What would you recommend should be done to improve protection?
The wall and fence has been broken down so animals could get in and contaminate the area around the pump. The stone wall and wooden fence should be repaired and a gate fitted so that people can gain access but animals cannot.