Groundwater lies hidden and invisible under the surface of the earth and builds an almost area-wide source for the drinking water supply in the RBD Weser, wherefore the protection of this resource represents an important task for the water management.

In the North German lowland, partly very powerful pore aquifers were formed in river gravels and sands sedimented during the glacial period, whereas in the south bedrock area cleft and karst aquifers are present. Groundwater is exposed to pressures from pollutant inputs, especially nitrate and pesticides, which enter the groundwater mainly diffusely, from lands used for agriculture. Permanent exchange between the groundwater and rivers and lakes on the surface also contributes to the diffuse pollution spreading in these surface waters.

Naturally pollutants in groundwater are metabolized very slowly. Therefore, especially sustainable and forward-looking attention must be paid to the protection from input. The European Commission has took account of this 2006 and issued, additionally to the EC Water Framework Directive, a Daughter Directive on Groundwater (Directive 2006/118/EC), establishing the environmental standards for nitrates and pesticides as well as further threshold values, in order to describe the good groundwater status and to achieve, respectively fall below these values until 2027. Current status is described in the Management Plan of the RBD Weser 2009.