Reservoir levels and rainfall figures

Last reviewed:

From 1-31 July, rainfall across the Thames catchment was 35% of the 134 year historic monthly average, with 20.5mm.

Rainfall in the last year

The graph below shows the rainfall over the last year and percentage increase and decrease against the monthly average.

Rainfall percentages for the last 12 months in relation to long term average rainfall

Where our water comes from

Across our region, we take about 65 per cent of our source water from rivers, in a process called abstraction. We then store this in large, open reservoirs (known as surface reservoirs) before putting it through our treatment process to turn it into drinking water.

The remaining 35 per cent comes from natural underground reservoirs called aquifers, from which we pump water using boreholes. This water has originally fallen as rain and sunk down into the ground in a process called recharge. These supplies from aquifers are referred to as groundwater.

Find out more about where our water comes from

Reservoir and water levels

The diagram below shows the rainfall and levels of water in the rivers, aquifers and reservoirs in our area, for the last month.

Reservoir and rainfall diagram

Water situation summary

On 31st July, the Thames Regional Soil Moisture Deficit (SMD) total was 114 mm which is higher (i.e. drier) than expected for the time of year.

At the end of July, groundwater levels were generally Normal, with some exceptions. An area of the Lee Chalk in North East London, an area of the Guildford Lower Greensands and an area of the Chilterns were Below Normal, whereas an area of the Cotswolds was Above Normal.

Generally, river flows were below their long term averages in July. The Teddington Target Flow was maintained at 800 megalitres/day until 06 July 2018, where it was decreased to 700 megalitres/day in agreement with the Environment Agency.

Reservoir storage on the 31st July 2018 for London as a whole was 80% (West London 82% & Lee Valley 71%) and Farmoor storage was 98%.