Thames water situation: December 2025 summary
Updated 14 January 2026
Applies to England
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1. Summary
Thames area received 90mm of rainfall in December, which was 118% of the long term average (LTA). Soil moisture deficits (SMD) decreased across Thames area to 9mm, which is below average for the time of year. The majority of monthly mean river flows were normal for the time of year. Groundwater levels have risen at 8 of our indicator sites. The majority are normal for the time of year however levels range from normal to exceptionally high. Farmoor reservoir is above average for the time of year, while the Lower Thames reservoirs are below average.
2. Rainfall
Thames area received 90mm of rainfall in December, 118% of the LTA. Thames area had a north-west, south-east split, where areal units towards the north and west had above normal rainfall, while units in the south and east received normal rainfall. The majority of the month’s rain fell in the first 3 weeks of December, with the Christmas period being relatively drier. The wettest day was 18 December where just under a quarter of the month’s rain fell. So far this winter period (October to December) 111% of expected rain has fallen.
3. Soil moisture deficit and recharge
SMD decreased to 9mm in December, which is below the average of 12mm. Effective rainfall across Thames area is 84%, with 4 areal units (Cotswolds West, Cotswolds East, Berkshire Downs, and Cherwell) having greater than 100% effective rainfall. However, 4 areal units (Loddon, Lower Wey, Ock, and Cut) still have not had any effective rainfall due to higher SMDs.
4. River flows
Monthly mean river flows increased at all indicator sites in December. The majority of sites are normal for the time of year, while, 2 are above normal (Wey at Tilford and Thames at Kingston (Naturalised)), and 4 are notably high (Cherwell at Banbury, Evenlode at Cassington, Coln at Bibury, and the Thames at Farmoor (Naturalised)).
5. Groundwater levels
Groundwater levels increased at 8 of our indicator sites in December, with the majority at normal levels for the time of year. Fringford (Great Oolite) and Jackaments Bottom (Inferior Oolite) are now above normal, Rockley (Chalk) has returned to normal, while the Flashes (Lower Greensand) remains at exceptionally high. Levels continued to decline at Stonor Estate (Chalk), but remain normal for the time of year. Levels at Frith Cottage (Lower Greensand) and Ampney Crucis (Great Oolite) have slightly declined, however both sites are above normal.
6. Reservoir stocks
Reservoir stocks in Farmoor increased from 92.6% to 97.2%, while the Lower Thames reservoirs also increased from 70.6% to 85.4%. Farmoor was above the LTA for December, however the Lower Thames was still below.
7. Environmental impact
During December 51 flood alerts, and 1 flood warning were issued on rivers in the Thames area. At the end of December, 0 abstraction licences were being constrained in the area to protect water resources and 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.