Research and analysis

Wessex 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 a relatively dry month with an average of 38mm rain falling across Wessex, 57% the long term average (LTA). Rainfall was generally below normal across Wessex with only the Dorset Stour hydrological areas receiving normal rainfall. The previous 3-month period has been the second driest July to September on record (43% LTA). The previous 6 months have been the third driest April to September on record (59% LTA). Soil moisture deficit (SMD) for the Wessex region showed some early recovery but increased again by the end of the month to a historic maximum for this time of year. Daily mean flows across Wessex remained low throughout the month with little response to rainfall. The majority of sites across Wessex reported below normal to exceptionally low monthly mean flows with the River Tone and Bristol Frome at a historic low for September. Groundwater levels fell across much of Wessex during September. All sites were notably or exceptional low by the end of the month except Allington which was normal. Most sites on the Chalk Aquifer are reporting as notably low or exceptionally low. Wrington (Carboniferous Limestone) is also reporting exceptionally low at the end of the month. Reservoir storage has reduced with Wessex Water ending the month at 28% total storage capacity, significantly below 1976, 2022 and 2025. Bristol Water ended the month at 44% total storage capacity similar to 2025.

2. Rainfall

An average of 38mm of rain fell across Wessex in September (57% of the LTA). One third of the month’s total rainfall was recorded on 7 September. Rainfall was generally below normal across Wessex except for the Upper and Middle Dorset Stour hydrological areas which received normal rainfall for September. The Upper Dorset Stour hydrological area received the highest monthly total of 49mm, equivalent to 74% of the LTA.

The previous 3 months saw exceptionally low rainfall across the Wessex region, being the second driest July to September on record. The previous 6 months saw exceptionally low rainfall in all areas except 2 in the north which were notably low. The last 12 months, however, show normal to above normal levels of rainfall with the south of the Wessex being wetter than the north. September marks the end of the water year which started with the sixth wettest October to March followed by the third driest April to September.

3. Soil moisture

SMD decreased sharply at the start of September in response to rainfall at the end of August and early September. This increased again towards the end of the month, exceeding the historic maximum. SMD at the end of the month is much higher than in 2025. Most hydrological areas in the south-east of Wessex recorded a SMD between 131mm to 160mm at the end of September, while most areas to the north and west recorded a SMD between 101mm to 130mm. The east of Wessex was 51mm to 75mm greater than the LTA.

4. River flows

Daily mean river flows remained low across Wessex throughout September in response to the relatively low rainfall. This is most noticeable on the monitoring sites on the Hampshire Avon and Dorset Stour that reported notably low to exceptionally low daily mean flows at the end of the month. Sites in quicker responding catchments in the north of Wessex showed temporary response to rainfall in early September but nothing sustained.    

The majority of monitoring sites across Wessex reported below normal to exceptionally low monthly mean flows for September. Only the River Isle at Ashton Mill and River Asker at Bridport East Bridge in the west reported normal monthly mean flows. Almost all sites in chalk catchments reported notably low to exceptionally low monthly mean flows. In the north of Wessex both Bristol Frome at Frenchay and River Tone at Bishops Hull reported the lowest monthly mean flows on record for September. These were 20% and 45% LTA respectively.  

5. Groundwater levels   

Groundwater levels continued to fall across Wessex during September. Most monitoring site recorded notably or exceptionally low by the end of the month. Allington was the only site to report normal groundwater levels.

Didmarton experienced a marked decline during September, falling from normal levels at the end of August to notably low by the end of the month. Half the sites on the Wessex Basin Chalk were exceptionally low and have shown no response to the rainfall. Wrington (monitoring the Carboniferous Limestone) was also reporting exceptionally low.

6. Reservoir storage

Reservoir storage has continued to fall through September for both Bristol Water and Wessex Water due to the lack of rainfall. Wessex Water ended the month at approximately 28% total storage capacity, significantly below 1976, 1995 and 2025. Bristol Water was at 44% total storage capacity at the end of September and is tracking at a similar storage to 1995.

Author: Wessex Hydrology, hydrology.wessex@environment-agency.gov.uk

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.