Water source selection
The quantity, quality, and reliability of available water are three main factors that need to be considered when evaluating water sources. Socio-cultural and technical issues may also be important. This section provides an overview of some of these different factors.
If you were selecting a new source of water for a community you would need to be sure that the volume of water that could be supplied would be sufficient to meet the community’s needs, both now and in the future. It would also be important to consider the reliability of the source over time.
The quality of water required depends on what it will be used for. Drinking water must be clean and safe to drink and protected from any contamination by pathogens or other pollutants. The primary concern must be to prevent the transmission of waterborne diseases. For other water uses such as for domestic washing or for agricultural or industrial uses, the quality is less critical.
In general, surface water sources are likely to contain many different materials and potential pollutants. These include micro-organisms, some of which may be pathogens, and small solid particles referred to as suspended particulates or suspended solids. These make the water turbid (Figure 4.8). Turbidity (the cloudiness of water) is a measure of water clarity. Turbidity is considered a useful approximate measure of water quality because pollutants and micro-organisms can be carried on the surface of suspended solids. The more turbid or cloudy the water is, the more suspended particles there are in it, and the more polluted the water is likely to be. It is important to realise, however, that clear water is not necessarily clean, because some contaminants may not be visible.
Why is surface water likely to be turbid?
Surface water is highly vulnerable to turbidity because solid particles of soil are washed off the land in run-off that flows to river and lakes, especially by heavy rains.
Surface water is easily polluted and can be affected by wide seasonal variations in turbidity. As a water source, surface water is often the easiest to access, but large quantities of suspended solids make it difficult to treat effectively. In general, groundwater is less likely than surface water to be polluted by pathogens or solid particles because the water is cleaned to some extent as it percolates down into the rock. However, it may have higher concentrations of dissolved substances. This means that groundwater has less microbial contamination but the dissolved substances and minerals, such as fluoride, may have significant effects on its quality.
Fluoride in drinking water is a well-known health concern. In some parts of Ethiopia concentrations in groundwater exceed the World Health Organization guideline of 1.5 mg/l (milligrams per litre). The highest concentrations, which can be greater than 10 mg/l, are found in waters from the Rift Valley zone. For people living in this area, dental and skeletal fluorosis are significant public health problems causing brown patches on the teeth, joint pain, limited movement of joints and, ultimately, crippling.
The National Fluorosis Mitigation Project has responsibility for planning a national strategy to deal with this problem. Several methods of defluoridation (removing fluoride from water) using chemicals or bone char have been successfully trialled at community and household levels (Osterwalder et al., 2015; Abaire et al., 2009; Esayas et al., 2009). However, selecting an affordable and sustainable standard technology for widespread use is challenging. Yang et al. (2015) found there is no single, preferable method for fluoride removal in Ethiopia because selection depends on the specific conditions of each location and on the preferences of the people involved.
Socio-cultural considerations may be important for water source development. Before a new water source is developed, a thorough assessment of the needs and wishes of the community should be undertaken, involving all groups of people including women, men, and children, members of any distinct social groups, disabled persons, and other vulnerable groups. It is particularly important that women participate in the process because they are likely to have the most knowledge about existing sources and are most likely to benefit if new supplies are developed. If the community’s opinions are not taken into account, the water supply system is likely to be under-used and may easily fall into disrepair, causing people to revert to their old water sources which may be more polluted.
Case Study 4.1 Hadera and the community who would not drink the blood of their forefathers
Hadera is a senior WASH expert working as a water and sanitation coordinator in small rural town. The town’s inhabitants had been suffering from a critical lack of sufficient safe water supplies and from waterborne diseases. Hadera had a good connection with the manager of an international non-governmental organisation (INGO), and convinced him to develop a water supply scheme for the needy community. The INGO finally managed to dig a well and get a good yield of water, and was able to handover the new facility to the kebele leadership for community use. Unfortunately, the community refused to use the water supply as their drinking water source. The INGO was surprised and asked them why not, mentioning the huge investment put into developing the water point in order to support the community. The community replied ‘we will not drink the blood of our forefathers’. The water source was developed in an area that served as a burial place many years ago and the villagers believed that the water contained the blood of their ancestors and so would not drink it.
What should Hadera and the INGO have done differently?
The problem could have been avoided if the villagers had been involved and consulted in the process of the water source development.
The development of the source must be technically feasible and the operation and maintenance requirements for the source abstraction and supply system must be appropriate to the resources available. Supply systems are likely to be misused if they cannot be operated and maintained either by community members or by organisations and institutions within the area.People who have responsibility for the maintenance of water sources or distribution points should be properly trained and rewarded for their contribution, to ensure sustainability.