4.4.2  Water quality

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.

Figure 4.8  The brown colour of river water is caused by the suspended solids carried in the flow.

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

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.