Wessex water situation: August 2025 summary
Updated 12 September 2025
Applies to England
© Crown copyright 2025
This publication is licensed under the terms of the Open Government Licence v3.0 except where otherwise stated. To view this licence, visit nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: psi@nationalarchives.gov.uk.
Where we have identified any third party copyright information you will need to obtain permission from the copyright holders concerned.
This publication is available at https://www.gov.uk/government/publications/water-situation-local-area-reports/wessex-water-situation-august-2025-summary
1. Summary
August was the sixth consecutive dry month in Wessex. An average of 39mm of rain, 54% of the long term average (LTA), fell across Wessex. Most rain fell between 27 and 31 August at the end of the month. This has now been the second driest 6-month period (March to August) since records began in 1871. The north of Wessex received notably less rain in August than in the south. For several hydrological areas in the north, this has been the driest 6-month period (March to August) on record. Soil moisture deficit (SMD) increased gradually throughout most of August but fell sharply in the last week of the month following the rain.
Monthly mean flows recorded across Wessex in August were largely below normal or notably low. Daily mean flows in August peaked towards the end of the month, in response to rain between 27 and 31 August. Most groundwater sites, including all sites monitoring the Chalk aquifer, reported notably or exceptionally low levels at the end of August. The only exception was Allington in the north which reported below normal levels. Overall reservoir levels for Wessex Water were approximately 42% capacity at the end of August, while levels were approximately 39% capacity for Bristol Water.
2. Rainfall
An average of 39mm of rain fell across Wessex in August (54% of the LTA). This is the sixth consecutive dry month, resulting in the second driest 6-month period (March to August) since records began in 1871 and the driest since 1976. However, for several catchments in the north of Wessex such as the Bristol Avon and the Mendips, this is the driest 6-month period (March to August) on record. In total, 84% of the month’s rain fell between 27 and 31 August. Overall, rainfall was notably low in most hydrological areas in the north and either normal or below normal in most areas to the south. the highest relative rainfall fell in the Poole Harbour and Purbeck area with 80% of the LTA. The Little Avon in the north of Wessex received the least relative rainfall with 34% of the LTA.
Over the past 3 months, the majority of hydrological areas in the north and west of Wessex received notably low rainfall while the majority of sites in the south received below normal rainfall. Over the past 6 months, all hydrological areas have received exceptionally low rainfall. However, over the past 12 months, all areas have received normal rainfall.
3. Soil moisture
SMD in Wessex continued to increase for most of August, spending the majority of August close to the historic maximum SMD. However, due to the rain in the last week of August, SMD decreased rapidly at the end of the month. At the end of August, SMD was notably lower than the historic maximum and only slightly higher than this time last year. Across most hydrological areas, SMD ended August between 101mm to 130mm. The other areas all ended August with an average SMD between 71mm to 100mm. For all but 2 hydrological areas, SMD at the end of August was between 6mm to 25mm greater than the LTA.
4. River flows
In August, most flow sites in Wessex recorded below normal or notably low monthly mean flows. The only exceptions were Frenchay on the Bristol Frome to the north and South Newton on the Wylye to the south which both recorded exceptionally low mean flows during August. Most sites monitoring flows on or downstream of the Chalk aquifer recorded slightly higher relative monthly mean flows because of supporting baseflow from the aquifer. Daily mean flows across Wessex peaked toward the end of the month around 29 August following the rain on the previous 2 days with most flows starting to recede at the end of the month.
5. Groundwater levels
Following 6 consecutive dry months, the majority of groundwater sites in Wessex, including all sites monitoring the Chalk aquifer, ended August reporting notably or exceptionally low levels. Allington (monitoring the Great Oolite) was the only site to record below normal groundwater levels at the end of August. For most monitoring sites, groundwater levels decreased throughout August.
6. Reservoir stocks
Both Wessex Water and Bristol Water reservoir levels continued to decrease throughout August. The combined levels at the end of the month for Wessex Water were approximately 42% capacity while for Bristol Water, combined levels were approximately 39% capacity. For both water companies, this is notably lower than reservoir levels recorded this time last year.
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.