In many European countries, citizens are obliged to connect their home sanitation to the national sewerage system where possible. This has resulted in large percentages of the population being connected to a sewerage system. For example, the Netherlands have 99% of the population connected to the sewerage system, and 1% has an individual sewage disposal system or treatment system, e.g., septic tank. Others have slightly lower (though still substantial) percentages; e.g., 96% for Germany.
Sewerage systems often reduce the water table in areas, especially in densily populated areas where rainwater (from house roofs) is directly piped into the sewerage system as opposed to being simply allowed to be absorbed by the soil. In certain areas it has resulted in a significant lowering of the water table. In the example of Belgium, a lowering of the water table by 100 meters has been the result. The freshwater that is accumulated by the sewerage system is then piped to the sea.