The water within the chalk aquifer of Southern England is replenished by rainfall that lands on the exposed chalk hills of the North and South Downs and the Chilterns. Normally recharge takes place during the winter months when potential evapotranspiration is low and soil moisture deficits are negligible. Groundwater amounts vary seasonally, with levels rising from autumn through winter into spring. During the summer months, potential evapotranspiration generally exceeds rainfall, soil moisture deficits build up, and little, if any, percolation takes place.
In the summer, water still leaves the chalk from springs as well as by abstraction from boreholes. This pattern is not constant, since rainfall varies both over time and location. Rivers fed by groundwater from chalk aquifers can have intermittent sections.
Some of the most acute problems with over-abstraction have been found in chalk stream systems, where up to 95% of the flow is derived from underground aquifers. The abstraction has reduced the flow in many chalk streams and, in some cases, have completely dried up sections of these important rivers, especially during dry summers when public demand is at its highest. This also has economic impact on local communities, resulting in the inability to fish.