Groundwater is the accumulation of water in the ground that seeps into the ground from precipitation or sometimes from lakes and rivers. Humans can negatively influence the quality of the groundwater through their activities in industry and business. For example, through the pollutants in the air, fertilizers and pesticides from agriculture or through highly concentrated pollutants from contaminated sites. Other causes of groundwater pollution include illegal landfilling of water-soluble household waste and effluent from leaky pipes and sewers.
When water is obtained through groundwater extraction, the water should therefore be treated before it is used. The most common treatment processes are ventilation, mechanical filtration, softening and disinfection. When aerating the groundwater, carbonic acid and hydrogen sulfide are expelled and at the same time insoluble flakes are formed from dissolved iron and manganese compounds, which are further separated together with suspended matter by mechanical filtration. Water that is too hard can be softened by decarbonization or ion exchange. Lime milk, which precipitates calcium carbonate dissolved in the water, is used in the decarbonization process. During ion exchange, calcium and magnesium ions dissolved in the water are usually replaced by sodium ions. In order to remove harmful germs and bacteria, water still has to be disinfected. Chlorine compounds, ozone or UV radiation are typically applied.