Thames water situation: May 2026 summary
Updated 11 June 2026
Applies to England
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Another dry month saw Thames area receive 25mm of rainfall in May, 47% of the long term average (LTA). Rainfall over the meteorological spring (March to May) was exceptionally low across the majority of the area, and soil moisture deficits (SMDs) increased significantly in response. Monthly mean river flows decreased at all of our indicator sites and were mostly below normal. Groundwater levels continued their seasonal decline – with the majority ending the month normal for the time of the year.
1. Rainfall
Thames area received 25mm of rainfall in May, 47% of the LTA. The majority of our areal units in the area were notably low, with only the Cotswolds West unit ending the month normal. The meteorological spring (March to May) ended very dry, as the majority of Thames area received exceptionally low rainfall over the last three months. The 3 highest daily totals were all recorded in the Cotswolds West unit on the third and eighth of the month and ranged between 12mm and 14mm.
2. Soil moisture deficit and recharge
Below average rainfall and warm temperatures during the month allowed the soil moisture deficit (SMD) to grow significantly and end the month at 89mm, much higher than the LTA (49mm). The highest SMD was calculated in the Cut catchment (99mm) and the lowest in the Cotswolds West (56mm). Due to the prevailing dry conditions, there was no significant effective rainfall across most of our areal units.
3. River flows
Monthly mean rivers flows across Thames area reflected the drier conditions of previous months and decreased at all our indicator sites in May. By the end of the month, 11 out of 15 sites were below normal or lower. Flows on the River Wey, supported by the Lower Greensand aquifer, remained resilient.
4. Groundwater levels
Groundwater levels continued their seasonal decline at all our indicator sites in May, although they mostly remained normal for the time of the year. The exceptions were Jackaments Bottom (notably low, Inferior Oolite), Frith Cottage (above normal, Lower Greensand) and Flashes (notably high, Lower Greensand).
5. Reservoir stocks
Farmoor Reservoir ended the month at 98.6%, above the LTA for the time of the year whereas the Lower Thames Reservoirs ended the month at 89.7%, below the LTA.
6. Environmental impact
At the end of May, 8 abstraction licences were having their flow constrained in order to protect the environment.
Author: Thames Area Groundwater Resources and Hydrology, enquiriesWT@environment-agency.gov.uk
Contact Details: 030708 506 506
All data are provisional and may be subject to revision. The views expressed in this document are not necessarily those of the Environment Agency. Its officers, servants or agents accept no liability for any loss or damage arising from the interpretation or use of the information, or reliance upon views contained in this report.