Research and analysis

Wessex water situation: December 2025 summary

Updated 14 January 2026

Applies to England

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

1. Summary

December was a second consecutive wet month with an average of 141mm of rain in Wessex, 139% of the long term average (LTA). Most rain in December fell towards the beginning and the middle of the month with little to none after 21 December. Soil moisture deficit (SMD), decreased through most of December but rose slightly at the end of the month due to the dry weather. Monthly mean flows recorded across Wessex in December were largely notably to exceptionally high except for in the Hampshire Avon catchment where flows were normal. Daily mean flows for most sites peaked earlier in the month and fell towards the end of December in response to the drier weather. Most groundwater sites on the Chalk aquifer reported normal levels at the end of the month. Groundwater levels in the rest of Wessex were largely normal or above normal. The 2 outliers were Kingston Russell Road (monitoring the Chalk) and Didmarton (monitoring the Inferior Oolite) which both recorded notably high levels. Overall reservoir levels for Wessex Water were close to 100% capacity at the end of December while for Bristol Water, levels were approximately 90% capacity.

2. Rainfall

An average of 141mm rain fell across Wessex in December (139% of the LTA). Most rain fell during two periods in the month, with 47% of the month’s rain between 1 and 8 December and another 48% of the month’s rain fell between 14 and 21 December. The highest relative rainfall was recorded in the Dorset Frome and West Dorset Streams which both received 169% of the LTA. The lowest relative rainfall was recorded in the West Somerset Streams which received 113% of the LTA. In December most hydrological areas in Wessex received above normal rainfall except for 4 hydrological areas to the south and west which received notably high rainfall and the West Somerset Streams and Mendips and Chew areas which received normal rainfall.

Over the past 3 months, most hydrological areas received above normal rainfall except for 4 which were notably high and 2 where were normal. Over the last 6 months, most areas of Wessex received normal rainfall except for a few areas to the north and south which received above normal rainfall. In the last 12 months all areas received normal rainfall.

3. Soil moisture

Soil moisture deficit (SMD) decreased through most of December but started to rise during the dry last week of the month. At the end of December SMD for Wessex was under 10mm for almost all of Wessex except the Bourne and Lower Hampshire Avon which were between 10mm to 20mm. SMD at the end of December was within 5mm of the LTA for most hydrological areas in Wessex except for the Lower Hampshire Avon and Wylye and Nadder areas where SMD is between 6mm to 25mm greater than the LTA.

4. River flows

In December, most flow sites in Wessex recorded either notably or exceptionally high mean flows. Both the Dorset Frome at East Stoke Combined and Dorset Stour at Hammoon recorded the highest monthly mean flows for December on record. The main exceptions were flow sites in the Hampshire Avon catchment and the Bristol Avon at Bathford which recorded normal flows. The Hampshire Avon at Amesbury and the Wylye at South Newton were the only sites to record monthly mean flows below 100% of the LTA due to lower groundwater levels in the Salisbury Plain area. Daily mean flows for most sites peaked earlier in the month and fell towards the end of December in response to the drier weather.

5. Groundwater levels   

At the end of December, the majority of groundwater monitoring sites on the Chalk aquifer recorded normal levels. The exception was Kingston Russell Road to the south west of the aquifer which recorded notably high levels. While within the normal banding, Tilshead remains notably lower than other sites monitoring the Chalk and was close to returning to below normal at the end of December. Sites monitoring other geologies reported between normal and above normal levels at the end of the month except for Didmarton (monitoring the Inferior Oolite) which recorded notably high levels. Groundwater levels across most sites were rising for most of December but levelled off or started to fall at the end of the month in response to the drier weather.

6. Reservoir stocks

Both Wessex Water and Bristol Water reservoir levels increased during December. The combined levels at the end of the month for Wessex Water were close to 100% capacity while for Bristol Water, combined levels were approximately 90% capacity. For Wessex Water levels are similar to this time last year while for Bristol Water they are slightly lower.

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.