It is possible that boreholes pumping large amounts of groundwater cause stream flow to reduce, however there may also be natural reasons for low stream flows.

Most rivers get their flow from a combination of water that runs over the ground surface (runoff) and water that flows underground and seeps through the sides and base of the river (groundwater). Surface runoff occurs mainly in winter, is intermittent and of relatively short duration. In summer and autumn, when river flows are low, much of the flow is groundwater from the underlying aquifer.

Rivers draining areas that consist entirely of permeable rocks (e.g. the Chalk downlands of southern England) obtain virtually all their water from aquifers. Flows are at a maximum at the end of winter or in early spring, when groundwater levels are high, and decline progressively from late spring to autumn. In Chalk aquifers, as the water table falls, streams may dry up as the point at which the river bed intercepts the water table migrates downstream. The upland sections of these streams, referred to as winterbournes (or simply bournes), may remain dry for extended periods during droughts.

Pumping large volumes of groundwater near to a stream may affect its flow by reducing the amount of water flowing into the river or altering the direction of groundwater flow causing water to flow from the river towards the pumping borehole. Reduced flows in a river may affect it as a habitat for wildlife or its ability to dilute the outflow from sewage treatment works (although in many streams the treated outflow from these works helps to maintain flow).

However, it’s often difficult to say how much the reduced river flows that occur at times are due to pumping and how much they are due to natural changes in the water-table. Where it is recognised that groundwater pumping is having a negative effect on particularly important stretches of river, water companies work together with the environment regulators to find ways of improving the flow.

If you are concerned about the flow in a local river contact the Environment Agency in England and Wales, the Scottish Environment Protection Agency in Scotland, or the Environment and Heritage Service in Northern Ireland.