Thames Water · overflow TWL00648
Monitor offline
Recorded by the operator as Dollis Brook.
The Environment Agency data shows this overflow's monitor (operator listed as Thames Water) as offline (status timestamp in the public data: 20 Aug 2026 at 10:42 UTC); while offline the data cannot show whether it is spilling.
📍 51.64207°, -0.19953°
8
spill events
1466h
cumulative discharge
9 weeks
longest single event
2026-06-11
first event on record
In the last 30 days this overflow recorded 0h of discharge. Thames Water has 43 of its 577 monitored overflows reporting spills in this 30-day window.
9 other overflows discharge into the Dollis Brook. 1 has its monitor offline. Combined recorded discharge in the last 30 days: 2h.
No spill events recorded in the last 30 days.
What the water company itself reported to the Environment Agency’s annual returns for this overflow, year by year. Hours are the total reported discharge duration; monitor working is the share of the year the event monitor was operating (a figure of 0% may mean no usable monitoring data rather than no spills). These figures are the operator's own reporting, not our measurement, and our live record above begins on 6 May 2026.
| Year | Spills counted | Hours | Monitor working | Matched by |
|---|---|---|---|---|
| 2024 | 67 | 279h | 98% | hub id |
| 2025 | 39 | 112h | 100% | hub id |
2024, the operator's stated reason: "N/A - Ongoing investigation"
2025, the operator's stated reason: "Not asset maintenance - Hydraulic capacity"
Source: Environment Agency, Event Duration Monitoring storm overflow annual returns, all years. Matched to this overflow by hub id.
The nearest Environment Agency rain gauge, Hornsey, is 8.0 km from this overflow. It recorded 3.8 mm in the last 48 hours.
| Day (UTC) | Rain |
|---|---|
| 17 Oct 2026 | 0.4 mm |
| 16 Oct 2026 | 3.4 mm |
| 15 Oct 2026 | 0.0 mm |
| 14 Oct 2026 | 0.0 mm |
| 13 Oct 2026 | 0.6 mm |
| 12 Oct 2026 | 0.2 mm |
| 11 Oct 2026 | 0.0 mm |
Rainfall comes from 15-minute Environment Agency readings rolled into hourly and daily totals; the 48-hour figure rests on 183 of 192 possible readings. The gauge is 8.0 km from this overflow, so it may not match the rain at the site itself, and the latest day may be incomplete. Rain figures do not show whether a discharge was permitted; that is a matter for the regulator. How we keep the record.
Latest readings at the Environment Agency gauge "Whetstone", on the Dollis Brook, which is 2.3 km from this overflow.
These are the Environment Agency's own gauge readings at the named station, shown for context. The station measures the river, not this overflow, and a reading does not show whether a discharge occurred or was permitted. Trend compares the latest reading with the one nearest 24 hours earlier; a change of 5% or less is shown as steady. How we keep the record.
No surface-water sampling points within 5 km.
The record above is verifiable from public Environment Agency and water-company data. Three official accountability channels — pre-filled with the evidence on this page.
If you can see foam, sewage debris, dead fish, or smell something wrong — submit a citizen report. Confirmed reports are added to the Truth Engine and strengthen the public record on this overflow.
📷 Report what you saw →The official complaints route. Most companies require submission through their web form rather than email — open the form, then paste the pre-filled letter.
Subject: Storm overflow TWL00648 on the Dollis Brook: request for information Dear Thames Water, I am writing about storm overflow TWL00648 on the Dollis Brook. Environment Agency storm overflow monitoring data for overflow TWL00648 on the Dollis Brook (operator listed as Thames Water) records no spill events starting between 18 September 2026 and 18 October 2026. As of 18 October 2026 at 00:36 UTC, the monitor for this overflow is reported as offline (status timestamp in the public data: 20 August 2026 at 10:42 UTC). While a monitor is reported offline, the public data cannot show whether the overflow is spilling. Further details from the public record: - Open automated data flags on River Truth for this overflow: 1 (comparisons between public datasets, not findings of fault) - On the Dollis Brook, per the OS Open Rivers network (Ordnance Survey, Open Government Licence) - Location: 51.64207, -0.19953 - Sources: Environment Agency National Storm Overflow Hub and Water Quality Archive (Open Government Licence v3.0), cross-referenced via River Truth (https://rivertruth.co.uk/overflow/3978) These figures are taken from public monitoring data as published and may be revised by the publisher. They are not a finding that any permit condition has been breached. [Add your personal context here, for example how you use this stretch of water.] Please could you tell me: 1. Whether the monitoring record summarised above is accurate and complete 2. Why the monitor is reported as offline and when it is expected to report again 3. What work, if any, is planned at this overflow, and on what timeline 4. What measures are in place to reduce spills from this overflow in future [Delete if not applicable: I have copied the Environment Agency, Ofwat and my MP into this correspondence.] Yours faithfully, [Your name] [Your address] [Your customer reference if you are a Thames Water customer]
This overflow sits in the Chipping Barnet constituency — currently represented by Dan Tomlinson (Labour). Click below to open WriteToThem with the letter copied to your clipboard — paste it into the message box.
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Subject: Constituent query: storm overflow TWL00648 on the Dollis Brook Dear [your MP, WriteToThem will fill this in], I am writing as your constituent about public storm overflow monitoring data for our area. Environment Agency storm overflow monitoring data for overflow TWL00648 on the Dollis Brook (operator listed as Thames Water) records no spill events starting between 18 September 2026 and 18 October 2026. As of 18 October 2026 at 00:36 UTC, the monitor for this overflow is reported as offline (status timestamp in the public data: 20 August 2026 at 10:42 UTC). While a monitor is reported offline, the public data cannot show whether the overflow is spilling. Further details from the public record: - Open automated data flags on River Truth for this overflow: 1 (comparisons between public datasets, not findings of fault) - On the Dollis Brook, per the OS Open Rivers network (Ordnance Survey, Open Government Licence) - Location: 51.64207, -0.19953 - Sources: Environment Agency National Storm Overflow Hub and Water Quality Archive (Open Government Licence v3.0), cross-referenced via River Truth (https://rivertruth.co.uk/overflow/3978) These figures are taken from public monitoring data as published and may be revised by the publisher. They are not a finding that any permit condition has been breached. [Add your personal context here, for example how you and your family use this stretch of water.] I would like to ask: 1. Whether you support strengthening the regulatory regime for storm overflows, and monitor coverage in particular 2. Whether you would raise the monitoring data for this overflow with the Secretary of State for Environment, Food and Rural Affairs, the Environment Agency or Ofwat Yours sincerely, [Your name] [Your address (WriteToThem requires a postal address to verify your constituency)]
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For active pollution incidents — dead fish, foam, sewage on the riverbank — the EA hotline operates 24/7 and triggers a recorded investigation.