Research and analysis

Thames water situation: September 2025 summary

Updated 14 October 2025

Applies to England

• Publication for Northern Ireland
• Publication for Scotland
• Publication for Wales

1. Summary

Thames area received 69mm of rainfall in September, which was 121% of the long term average (LTA). Soil moisture deficits (SMD) decreased across Thames area; from 170mm in August to 160mm by the end of September. Monthly mean river flows were mostly normal for the time of year. Groundwater levels continue to decline at all but 2 of our indicator sites in September and ranged from notably low (Jackaments Bottom, Inferior Oolite and Ampney Crucis, Great Oolite) to notably high (Frith Cottage and Flashes, Lower Greensand). Farmoor reservoir and the Lower Thames reservoirs remained below the LTA for the time of the year.

2. Rainfall

September was a wetter month with the majority of the month’s rain falling over 3 days, the 2, 3 and 14 of September. Thames area received 69mm of rainfall in September, which was 121% of the LTA. All our areal units received either normal or above normal rainfall for the time of the year. The rainfall over the last 6 months, since April, was exceptionally low or notably low in all areal units, indicating a very dry summer. Thames area received 66% of the LTA rainfall that would be expected for the summer period (April to September).

3. Soil moisture deficit and recharge

SMD decreased across Thames area; from 170mm in August to 160mm by the end of September. This was still far above the LTA of 99mm for the time of year, indicating that soils are considerably drier than expected. As we enter the winter period, soils must become fully wetted before recharge to groundwater resources can happen.

4. River flows

Monthly mean flows increased at the majority of the key indicator sites compared to last month, in response to the wetter conditions. Despite this, monthly mean river flows at the majority of our key indicator were normal for the time of year. The River Coln at Bibury was the only indicator site to record exceptionally low flows due to groundwater levels in the oolites.

5. Groundwater levels   

Groundwater levels continued to decline at all but 2 of our indicator sites during September. Levels ranged from notably low at Jackaments Bottom (Inferior Oolite) and Ampney Crucis (Great Oolite), to notably high at Frith Cottage and the Flashes (Lower Greensand).

Most sites remained within the same banding as the previous month. However, Rockley (Chalk) rose from notably low to below normal, while Jackaments Bottom improved from exceptionally low to notably low.

Groundwater levels at Ampney Crucis and the Flashes have begun to rise, and the rate of decline has slowed across the remaining sites which is likely due to recent rainfall.

Overall, groundwater levels in the Oolites and Chalk are normal to notably low, whereas levels in the slower-responding Lower Greensand remain notably high for this time of year.

6. Reservoir stocks

Stocks in Farmoor reservoir increased from 81.6% to 87% during September. Reservoir stocks decreased in the Lower Thames reservoirs and ended the month at 63.6% compared to 66.6% at the end of August. Both the Farmoor reservoir and Lower Thames reservoirs remained below the LTA for the time of the year.

7. Environmental impact 

At the end of the month, 38 abstraction licences were being constrained in the area to protect water resources and the environment. There were also no flood alerts or flood warnings issued.

Author: Thames Area Groundwater Resources and Hydrology, enquiriesWT@environment-agency.gov.uk

Contact Details: 030708 506 506