Threats to underground water contamination

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 coliform. The presence of coliform in water indicates a high possibility of the presence of disease causing micro-organisms in water. Drinking water contaminated with faecal coliform can cause health problems such as diarrhoea, nausea, cramps, dysentery and hepatitis.

Sewage bursts

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. When the waste is decomposing, it produces a liquid called leach-ate which infiltrates into the ground when it rains, thus polluting groundwater. There is lot of companies and mines with unaligned dumpsites for liquid and solid matter. During the rainy season most of these overflow or they leach chemicals and minerals to the underground causing water contamination. There are cases of some areas around Zimbabwe where complaints have been filed by residents due to waste dumping affecting their ground water quality.

Building on wetlands

A wetland is referred to as any area of marsh, fen, peat land or water, whether natural or artificial, permanent or temporary with water that is static or flowing. Wetlands can be found near the banks of rivers, edges of lakes or in open fields and wooded areas where the water table is near surface. 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 sprouting new residential areas are built on wetlands and these wetlands 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.

Geological structure

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 water in 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. Examples of different water qualities caused by geological rock structure are: hardness of water, high salinity, high fluoride levels which causes rusty teeth, high levels of metals. Heavy metals such as lead, cadmium, and arsenic are bio accumulated in the human body and causes chronic diseases in low doses, and damage to the central nervous system in high doses. Some metals such as Cu, Fe, Co, Se, Mo, Mn, and Zn are needed in trace amounts as enzyme catalysts but in high doses these pose a health hazard to humans. Naturally occurring metals are dissolved in water when it comes into contact with rock or soil material.