Where our water comes from

We rely on rain to maintain groundwater levels in our region.

Groundwater is the water that soaks into our aquifers (underground layers of rock or unconsolidated materials through which water can flow and be stored). These supply up to 30% of the water we use every day across London and the Thames Valley. But that’s not all our aquifers do – they also help to keep our rivers flowing, which is where the remaining 70% of our water supply comes from.

Groundwater in the Thames region

Groundwater levels were average across the Thames region by the end of August, except in parts of the Cotswolds, where groundwater levels were between below and above average, and parts of the North Downs, where groundwater levels were above average.

Groundwater levels often respond slower to rainfall (or lack of it) than river flows providing resilience against short-sharp dry periods. Each aquifer has different properties and will respond in different ways.

River flow in the Thames region

By the end of August 2020, river flows in the River Thames and River Lee were average. Flows in the smaller rivers across the Thames region were generally average for the time of year, except for some rivers in the Cotswolds which were below average.

The Teddington Target Flow (TTF) was 800 Ml/d at the end of August. The TTF is the minimum River Thames flow over the Teddington weir that is required to balance environmental, navigational and water supply needs. The TTF depends on the time of year and our reservoir storage and is always agreed with the Environment Agency.

Saving for a rainy day

We store water in large, open raw water reservoirs before we pump it to our world-class treatment plants, ready for cleaning.

We carefully monitor water levels in reservoirs, regularly inspecting and maintaining the infrastructure to safeguard your supply.

At the end of August 2020:

Reservoirs in London were 88% full (86% full in West London and 95% full in Lee Valley)

Farmoor Reservoir in Oxfordshire was 94% full, which is average for the time of year

Our water resources situation

Check out our infographic to see our water resource situation at the end of August.