THREATS TO UNDERGROUND WATER CONTAMINATION
- Published: Wednesday, 07 June 2017 10:41
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There is an increase in borehole drilling and digging of wells in urban areas, especially in new residential areas because of unavailability of reticulated water services. In addition, there are no sewer services in these areas, construction of septic tanks evades local authorities’ by laws. Consequently, there is underground water contamination in some of the boreholes and wells.
In this regard, it is important for every household to know the quality of water they are drinking and using, to avoid adverse health effects. The drinking water should contain no harmful concentrations of chemicals or pathogens and ideally it should be aesthetically pleasing in regard to appearance, taste and odour.
Current threats to underground water quality
Septic Tanks and Latrines
There is rapid urban expansion happening in all towns in Zimbabwe. However, the rate of growth is way faster than the area infrastructural development and service provision. This is forcing people to construct their own septic tanks, latrines, boreholes and deep wells. Septic tanks have certain standards they should meet before they are deemed fit for use and this is to make sure that they do not leak and contaminate underground water. In most new residential areas, the stands are so small that construction of septic tanks or boreholes is not permitted by local authorities’ by-laws, but these are substituted by latrines and deep wells. Most of the septic tanks/latrines are not lined resulting in underground water contamination. There is stipulated distance of 30m upslope that should be between a water source and septic tank. The main form of contamination by septic tanks and latrines is of bacterial nature e.g. faecal coliforms. The presence of coliforms in water indicates a high possibility of the presence of disease causing microorganisms in water.Drinking water contaminated with faecal coliforms can cause health problems such as diarrhoea, nausea, cramps, dysentery and hepatitis.
Sewage pipe bursts are a threat to underground water quality. The main causes of sewage bursts are blockages and old piping systems that need to be replaced. The bursts are more pronounced in old high density suburbs in many cities were city council water supply is inconsistent. This has forced many people to construct their own deep wells and boreholes. When the waste from sewerage bursts is washed away during rains, there is contamination of boreholes and wells that are not well protected.
Dumping of Waste on Undesignated Areas
The dumping of waste on undesignated areas causes underground water contamination. Ehen the waste is decomposing, it produces a liquid called leachate which infiltrates into the ground when it rains, thus polluting groundwater. There are lot of companies and mines with unlined dumpsites for liquid and solid matter. During the rainy season most of these overflow or they leach chemicals and minerals underground causing water contamination. There are cases of some areas around Zimbabwe where complaints have been filed by residents due to waste dumping affecting ground water quality.
Building on Wetlands
A wetland refers to any area which is seasonally or permanently flooded with water. Wetlands can be found near the banks of rivers, edges of lakes or in open fields and wooded areas where the water table is high. It is in these open fields, wooded areas and river banks that people are now constructing their residential areas. One of the main importance of a wetland is water purification by improving water quality through filtering out contaminants, sediments, excessive nutrients and decaying matter. In Harare, most of the new residential areas are built on wetlands which have been purifying water for years. The residents then dig deep wells and boreholes for water supply, however, this water is affected by the contaminants that have been accumulated through filtration over years.
There is a relationship between the quality of water and the geological environment. The quality of borehole water at different locations differs depending with the underground soil type and the pollution levels in that environment.The natural underground rock type has an aesthetic effect on waterin regard to appearance, taste and odour. In some cases the geological environment is linked to chronic diseases such as renal failure due to the presence of lethal doses of metals.
What should be done?
Having realised that underground water quality is threatened by the above factors, it is important to ensure that your water is tested before you start using it. It does not follow that clear water is clean water. Getting your water tested ensures that you put it to the right use. For instance, if it is not safe for drinking it can be put to other uses such as irrigation.