Water that moves through the soil will, to some extent, be purified naturally. However, this is not always true because soil cannot remove all pollutants. Many soils have the ability to remove certain types of pollutants, including phosphorus, heavy metals, bacteria and suspended solids. However, pollutants that dissolve in water, like nitrate and ammonia from fertilisers and animal wastes, can pass through soils into the groundwater. This may cause high concentrations of pollutants in local drinking water wells. Leaking from underground storage tanks, solid waste landfills, improperly stored hazardous waste, careless disposal of solvents and hazardous chemicals on ground surfaces are other potential sources of groundwater pollution.
Why is it important for pit latrines to be located at least 15 metres from the nearest well and at a lower level?
Because, depending on the local geology, liquid from the pit could flow through rock and soil into the groundwater and to the well. If the latrine is at a lower level than the well, the effect of gravity will make groundwater contaminated from the pit flow away from the well.