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Reservoir levels

Reservoir levels and rainfall figures

How much rain falls in our region?

It may feel like it rains a lot in the UK, but did you know that our capital city gets less rain each year than Rome, Istanbul and even sunny Sydney?

The latest news on average rainfall and groundwater levels in the Thames region

In May, we saw significantly below average rainfall in the Thames Region. At 3.7 mm, it was 7% of the long-term average and the driest May on record.

On 31 May, the Thames Regional Soil Moisture Deficit (SMD) total was above average, meaning that the ground is drier than expected for the time of year.

Groundwater levels were generally above average across the Thames region by the end of May, except for the Cotswolds where groundwater levels were below average. Our groundwater levels have remained higher due to the properties of the aquifers, where our groundwater is stored, which makes the Thames Region more resilient to short-sharp dry periods than some other parts of the country. Each aquifer has different properties which is why, while groundwater levels in many areas of the Thames Region have remained higher after the winter rainfall, other areas, such as the Cotswolds, have seen levels decline more quickly with the dry weather.

Average rainfall in the Thames Region

Check out our graph to see average rainfall for the Thames Region.

Rainfall in the Thames Region graph

Where our water comes from

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

Groundwater is the water that soaks into our natural underground reservoirs called aquifers. 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.

River flow in the Thames region

During May 2020, river flows were generally below average across the Thames region, although some of the smaller river flows were average or above. This means that overall there has been less water in our rivers than expected during May.

The Teddington Target Flow (TTF) was maintained at 800 Ml/d during May. 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 May 2020:

  • Reservoirs in London were 92% full (93% full in West London and 89% full in Lee Valley)
  • Farmoor Reservoir in Oxfordshire was 99% full

Our water resources situation

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

Water resource situation diagram

Want to help save water at home?

There are lots of ways you can help save water, from turning the taps off when you're brushing your teeth, to using rainwater for your plants.

Learn more about saving water