An integral part of the Finnish landscape, eskers were formed at the end of the ice age around 10 000 years ago from the fine-grained material transported by the rivers flowing inside the ice. The faster the glacier retreated, the steeper and narrower the esker became. In addition to eskers, Finland has ice-marginal formations (Salpausselät) that are transverse to the retreating direction of the glaciers.
Eskers and ice-marginal formations are made of material that permeates water well and they are important groundwater areas. Sandy soil both purifies and stores water. Therefore the majority of domestic water is groundwater. Groundwater is easily contaminated as a result of human activity, for example when chemicals or road salt ends up in the soil. Water quality and quantity can be monitored by observation pipes installed in the ground.