Research and analysis

Wessex water situation: September 2025 summary

Updated 14 October 2025

Applies to England

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

1. Summary

An average of 95mm rain fell across Wessex in September, 142% of the long term average (LTA). Most of the month’s rain occurred within the first 2 weeks. Soil moisture deficit (SMD) initially decreased in September to close to the LTA, before rising again due to the drier period towards the end of the month. Monthly mean flows recorded across Wessex in September were largely normal. Daily mean flows peaked around 15 September following a period of rainfall across Wessex. The majority of groundwater sites, including most sites monitoring the chalk aquifer, reported below normal or notably low levels at the end of September. The exceptions were Tilshead and Kingston Russell Road which reported exceptionally low levels. At the end of September, reservoirs were at 36% and 37% capacity for Wessex Water and Bristol Water, respectively.

2. Rainfall

An average of 95mm fell across Wessex in September (142% of the LTA). Most rainfall occurred between 1 to 17 September (96% of the month’s rain), with the remainder of the month remaining relatively dry. The highest monthly rainfall was recorded at Cromhall in the Bristol Avon (224% of LTA). The lowest monthly rainfall was recorded at Bruton Dam in the Brue (101% of LTA).

All hydrological areas in Wessex received normal or above normal rainfall in September. Over the past 3 months, hydrological areas in Wessex received either below normal or normal rainfall. Over the past 6 months:

• 4 areas in Wessex including the Brue have received exceptionally low rainfall
• 9 areas including the Hampshire Avon have received notably low rainfall

The West Dorset Streams received normal rainfall over the past 6 months. Over the past 12 months (which constitutes the water year), most areas in Wessex received below normal rainfall. Rainfall over the last 7 months was 63% of LTA making it the fifth driest for this period on record.

3. Soil moisture

SMD in Wessex initially decreased at the beginning of September to the LTA. Following a period of dry weather, SMD increased again by the end of the month. Across most hydrological areas in Wessex, SMD was in the range of 71mm to 100mm at the end of September. SMD was between -5mm to 5mm difference to the LTA in south Wessex, the majority of north Wessex SMD was 6mm to 25mm greater than the LTA .

4. River flows

In September, most flow sites in Wessex recorded normal monthly mean flows. There were 3 sites in south Wessex within the chalk catchments which recorded below normal monthly mean flows in September. These are all supported by the chalk aquifer and reflects that groundwater is recorded between exceptionally and notably low. The Bristol Frome at Frenchay recorded as above normal monthly mean flows. Daily mean river flows responded to rainfall in the first 2 weeks of September. For the majority of Wessex, daily mean river flows began to reduce from 15 September due to decreased rainfall.

5. Groundwater levels   

Following 5 consecutive dry months between March and August, the majority of groundwater sites in Wessex, including most sites monitoring the Chalk aquifer, ended September reporting either below normal or notably low levels. Tilshead and Kingstone Russell Road (both monitoring the Chalk) were the only sites to report exceptionally low levels at the end of the month. For the majority of monitoring sites in Wessex, groundwater levels continued to decrease throughout the month. Groundwater levels increased at quicker responding sites Wrington (monitoring the Carboniferous Limestone) and Didmarton (monitoring the Inferior Oolite) during September.

6. Reservoir stocks

The majority of Wessex Water and Bristol Water reservoir levels recorded an initial increase in capacity in September, however by the end of September reservoir levels began to decrease. The exception was Clatworthy reservoir where capacity continued to decrease throughout September. The combined levels at the end of the month for Wessex Water were approximately 36% capacity while for Bristol Water, combined levels were approximately 37% which are lower than levels recorded this time last year and in 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.