Research and analysis

Kent and South London water situation: December 2025 summary

Updated 14 January 2026

Applies to England

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• Publication for Wales

In December, the Kent, South London and East Sussex (KSLES) area received 84% of long term average (LTA) rainfall, ranging from 63% in the Thanet Chalk to 103% in the Upper Mole catchment. December was characterised by early‑ and mid‑month rainfall peaks, with subdued totals thereafter. Soil moisture deficits (SMDs) declined across the majority of the area, with 4 of 13 remaining above LTA. The effective rainfall recorded in December was 60% of the LTA average.  Monthly Mean Flows (MMFs) were generally normal, though below normal flows were seen at the Wandle and the Ravensbourne due to clay geology and urbanisation. Groundwater levels ranged from exceptionally low at Chipstead and below normal at Sweeps Lane to normal levels at remaining groundwater sites. Reservoir stocks increased in December, with levels rising at all sites except Weir Wood Reservoir which stayed stable.

1. Rainfall

During December, the KSLES area received 84% of the LTA rainfall for the time of year, based on a whole-area average. Rainfall received in all catchments in the Kent South London and East Sussex area were normal except Thanet Chalk which was below normal. The percentage of LTA rainfall received ranged from 63% in the Thanet Chalk catchment in the East, to 103% in the Upper Mole catchment in the West. The highest daily rainfall total of 30.1mm was observed on day 18 of the month at Eden Vale sewage treatment works rain gauge in the Medway catchment.

Rainfall in December was generally highest at the start and again around the middle of the month, with much lower amounts throughout the remainder of the period. The top 5 highest rainfall days were 5, 17, 1, 29, and 3 December. December featured 3 dry days across the KSLES area, defined as a day with 0.2mm or less recorded rainfall. These dry days occurred on 23 December, 24 December, and 25 December, with 0.1mm recorded on 23 and 25 December, and 0mm on 24 December.

2. Soil moisture deficit and recharge

December SMDs were lower than November across most catchments, indicating a response to rainfall, while only a small number of catchments – Upper Mole, Medway, and Eastern Rother – showed slight increases from 0mm to 4mm. Dover Chalk remained unchanged between the 2 months. This decline was driven by the small but consistent wetter days and the effective rainfall received across the area during December, which amounted to 60% of the LTA. Overall, SMDs ranged from 0mm to 135mm at the end of December, compared with 0mm to 149mm at the end of November, highlighting the slight decrease month on month.

3. River flows

Monthly Mean Flows (MMFs) at key indicator sites in December were largely within the normal range across the area. Below normal flows persisted at the Wandle at Connolly’s Mill and the River Ravensbourne at Catford in the northwest. Both sites overlie clay‑rich geology, which restricts groundwater contributions, and are located in highly urbanised catchments where effective rainfall reaching the channels is limited. Consequently, the reduced flows observed are not unexpected for this time of year, given the combined effects of geology, land use, and effective rainfall patterns.

4. Groundwater levels   

Groundwater levels in the Chalk across the KSLES area ranged from exceptionally low to normal. Chipstead remained in the exceptionally low category throughout the month, with levels staying stable and ending December still classified as exceptionally low. Sweeps Lane registered below normal levels, while Wolverton, Little Bucket, Riddles Lane, and Fleete Reservoir all recorded normal levels for this time of year. Groundwater levels in the Greensand aquifer at Riverhead, in the central‑west of the area, were also within the normal range at the end of December, having eased slightly from above normal in November. Groundwater level variation this month broadly followed the pattern seen in November, with elevated SMDs in the west continuing to inhibit effective rainfall. Levels remained low at Chipstead, while sites across the rest of the area were generally stable or showed slight increases.

5. Reservoir stocks

Four out of five water company reservoirs in KSLES saw a rise in levels during December, Weirwood reservoir stayed stable throughout the month.

By the end of December, the reservoirs held by the following live storage capacities and LTA class:  

• Darwell – 65% normal
• Bewl – 59% below normal
• Bough Beech – 95% normal
• Powdermill – 78% normal
• Weir Wood – 100% above normal

6. Environmental impact 

There were 12 fluvial flood alerts and one fluvial flood warnings issued in December.

Author: Groundwater and Hydrology Team, ksl.gwh@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 in this report.