Serving parts of North West London and the Home Counties.

The Water Cycle


This image shows the journey that water takes to get to your tap.

 Water Cycle Infographic


The normal recharge period is between late October/November and March/early April.

This is when rainfall is most effective at replenishing the aquifer, resulting in a rise in groundwater levels. The chalk aquifer is where approximately 60% of our water for public supply comes from.

During the summer months when temperatures are higher and plants are using water, rainfall is less effective at recharging the aquifer. The exceptionally wet Spring and early Summer of 2012 did result in a rise in groundwater levels, but this was unprecedented.

We use a number of Environment Agency monitoring boreholes across our supply area to assess our water resources situation. We also have an extensive network of environmental monitoring associated with our National Environment Programme.

Our supply area is home to many chalk streams. These are globally rare habitats, rich in biodiversity. The upper reaches of a chalk stream are known as winterbournes, as they naturally dry out as groundwater levels decline.

When groundwater levels rise again, flow returns to this part of the river. Chalk streams have also been historically modified e.g. straightened, deepened, widened, which makes their habitat less suitable. We are working with the Environment Agency and other catchment partners to try and enhance and restore a number of chalk streams.

We made a customer commitment in our AMP6 Business Plan to leave more water in the environment to try and help benefit these chalk streams.

We have a Drought Management Plan which is an operational plan that we follow under drought conditions. View our Drought Management Plan.


Learn more about where our water comes from