Research and analysis

Hertfordshire and North London water situation: June 2026 summary

Updated 14 July 2026

Applies to England

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

The Hertfordshire and North London area (the Area) recorded 134% (70mm) of the long term average (LTA) rainfall for June. Soil moisture deficits (SMDs) continued to increase across the Area and ended June larger than the LTA. Monthly mean river flows were normal at the majority of our indicator sites except the River Roding at Redbridge (below normal) and the River Ver at Colney Street (above normal). Groundwater levels continued their seasonal decline at all of the Area’s indicator sites and they all ended the month with normal groundwater levels for June.

1. Rainfall

The Area recorded 134% (70mm) LTA rainfall for June. With the exception of Roding hydrological area which recorded normal rainfall, the remaining hydrological areas recorded above normal rainfall for the month. The Area recorded an average of 10 wet days (equal to or greater than 1mm rainfall). It was a month of 2 halves, a wet start with the first 11 days accounting for an average of 80% of the monthly total. The second half of June was largely dry with high temperatures. The exception to this is 22 June when a large thunderstorm occurred across southern England resulting in the highest daily rainfall total for the Area of 33.3mm recorded at Northolt rain gauge in the North London hydrological area. The summer period (April to June) has been overall much dryer than average as the Area recorded 61% (90mm) LTA rainfall. All of our hydrological units, except Roding (below normal), recorded notably low rainfall for the last 3 months.

2. Soil moisture deficit and recharge

Despite the larger than average rainfall in June, the dry weather the last couple of months combined with the hot, dry weather in the latter half of June resulted in SMDs continuing to increase across the hydrological areas. The Area ended June with an SMD of 126mm, an increase from May (99mm), which was larger than the LTA of 80mm. As expected for the time of year effective rainfall was only recorded in Chiltern East Colne and Lee Chalk hydrological areas in small quantities. The Area received a total of 2mm effective rainfall which was 104% LTA. For the summer period the Area had 19% of LTA (2mm).

3. River flows

Monthly mean river flows were normal at the majority (10) of our indicator sites. The River Roding at Redbridge recorded below normal flows while the River Ver at Colney Street recorded above normal monthly mean flows. As a consequence of healthy groundwater levels and above average rainfall in June, rivers in the Colne hydrological area recorded base flows near the top of the normal band with peaks in response to rainfall early in the month and the thunderstorm on 22 June. In the Lee hydrological area there was a general seasonal decline in base flows over the month. Most rivers remained in the normal banding except for the River Lee at Howe Green which just dropped into the below normal band towards the end of the month. The North London indicator sites recorded large peaks in flow in response to the thunderstorm on 22 June. However, the remaining clay and urban indicator sites recorded relatively smaller peaks in flow in response to the rainfall. No flood alerts or warnings were issued in June.

4. Groundwater levels   

Groundwater levels continued their seasonal decline at all 9 of the Area’s indicator sites and they all ended the month with normal groundwater levels for June.

5. Reservoir stocks

In the Lee Valley group, reservoir stocks remained steady during June with live capacity staying between 95% and 96%. Stocks ended the month above average level for the time of year at 95% of live capacity. In the Lower Thames group, the reservoir levels increased slightly at the beginning of June but then decreased to end the month with 88% of live capacity which was below the average level for the time of year.

6. Environmental impact 

In the Colne catchment, June Chalk river sources largely remained the same from their locations in May. In the Colne catchment, Chalk river sources moved slightly downstream from their locations in April. The:

• River Ver continued to flow downstream of Markyate but briefly ran dry downstream of Flamstead
• source of the River Gade remained at Hoo Lodge above Great Gaddesden
• River Bulbourne started flowing just upstream of Northchurch, below Dudswell Village.
• source of the River Chess remained at Missenden Road, upstream of Chesham
• River Misbourne was flowing downstream of Great Missenden, just above The Chiltern Hospital

The locations of Chalk river sources in the Upper Lee stayed largely the same as in May, with some moving slightly downstream. The:

• River Mimram was still flowing above Whitwell
• source of the River Beane remained just above Walkern
• River Rib flowed from Buntingford but flows reduced through Buntingford since last month from medium flow to low flow
• source of the River Ash (Herts) moved further downstream of Little Hadham to Winding Hill
• River Stort ceased flowing at Clavering since May as the source moved downstream to Stansted Springs

To protect the environment, during June a number of abstraction licence flow constraints were in force. This ranged between 4 and 9 per week, out of a month maximum of 33.

Author: Groundwater and Hydrology, groundwaterhydrology@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 within.