Research and analysis

Thames water situation: September 2026 summary

Updated 14 October 2026

Applies to England

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

1. Summary

September was another drier than average month. Thames area received just half of the long term average (LTA) rainfall for September. It was the driest 3-month period (July to September) and the driest summer (April to September) since records began. Soil moisture deficits (SMDs) were the highest ever recorded in this area for September. Monthly mean river flows remained similar to August, 4 indicator sites were recorded as normal for the time of year, while 8 sites recorded notably or exceptionally low flows. Groundwater levels continued their seasonal decline and ranged from notably low to notably high across Thames area at the end of September. Thames area remained in drought status, having entered drought in July.

2. Rainfall

Thames area received a total of 31mm of rainfall in September, 53% of the LTA for the month. Most of the rain fell on 5 separate days, 4 of which were in the first 2 weeks of the month. Rain on the 7 and 8 September accounted for 39% of the month’s rainfall, 13mm in total. Rainfall recorded was below normal for September in almost every hydrological area. Only the North Downs Hampshire hydrological area received normal rainfall compared to its LTA.

It has been the driest 6-month summer period (April to September) and the driest July to September in Thames area since records began. The area remained in drought status, having entered drought in July.

3. Soil moisture deficit and recharge

SMDs continued to increase throughout September, reaching levels considerably higher than would typically be expected for the time of year, with deficits roughly double their respective September LTAs across all hydrological areas. Effective rainfall was negligible during the month, with only 1mm recorded, equivalent to 27% of the September LTA. As we enter the winter period, soils will need to return to zero SMD before significant groundwater recharge can occur. The timing of this will depend on the rainfall received over the coming months.

4. River flows

Despite recent rainfall, monthly mean river flows for most of our reporting sites remained in the same banding categories as in August. Flows at 4 our indicator sites were recorded as normal for the time of year, while two-thirds (8 sites) recorded notably or exceptionally low flows. There were improvements at the River Thame at Wheatley and the River Loddon at Sheepbridge compared to August, each moving up one banding category to notably low and normal, respectively. Notably low flows were recorded on the River Thames at Farmoor (naturalised), the River Thames at Kingston (naturalised), the River Thame at Wheatley and the River Blackwater at Swallowfield. Exceptionally low flows were recorded at the River Thames at Kingston, the River Thames at Windsor, River Kennet at Calcot and River Coln at Bibury. The River Thames’s monthly mean flow at Kingston was the fourth lowest September monthly mean flow on record, after 1976, 1934 and 1990.

The West Berkshire Groundwater Scheme continued to operate throughout September, having been switched on at the end of August in order to supplement the flows in the River Thames and to bolster the water available for abstraction in the Lower Thames during the drought.

5. Groundwater levels   

Groundwater levels continued their seasonal decline at all indicator sites in September. At the end of the month, 6 of our 11 indicator sites remained normal or above for the time of year. Groundwater levels in the Lower Greensand aquifers continued to be relatively resilient, with The Flashes maintaining notably high levels for the time of year. The chalk and oolite aquifers are showing less resilience. In the chalk, levels at Long Sutton declined from normal in August to below normal in September, whilst Rockley dropped from below normal in August to notably low in September. However, Gibbets Cottage and Stonor Estate in the chalk remain at normal levels for the time of year. In the oolite aquifers in the west of the area, Jackaments Bottom and Ampney Crucis are both notably low for the time of year.

6. Reservoir stocks

In September, reservoir storage declined less rapidly than previous months. Farmoor Reservoir’s storage decreased to 69.0% at the end of the month, below the LTA for the time of year, down from 75.6% at the end of August. Storage in the Lower Thames Reservoirs also decreased, ending the month at 53.1%, also below the LTA, down from 59.4% at the end of August.

7. Environmental impact 

At the end of September, 51 abstraction licences were having their flows constrained to protect the environment, an increase from 41 licences at the end of August.

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

Contact Details: 03708 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 herein.