If you look up a property on the government’s long-term flood risk service, you may see that it’s in an area that ‘could be affected by flooding from reservoirs’. That can be a surprise, especially if there’s no reservoir in sight. Here’s what it means.
What the map shows
The reservoir flood maps show the area that could be flooded if a large reservoir failed and released its water. They’re produced for emergency planning, so they deliberately show a worst case. There are two scenarios: a ‘dry day’, when rivers are at normal levels, and a ‘wet day’, when a river is already in flood.
The maps don’t give a chance or probability. They show where water would go if the dam failed – not how likely that is.
How reservoirs are kept safe
In England, large raised reservoirs – those holding 25,000 cubic metres or more above the natural ground level – are regulated under the Reservoirs Act 1975. The Environment Agency enforces the law. Each reservoir must have a supervising engineer who keeps watch on it, and be inspected at regular intervals by an independent, specially qualified engineer. Any safety work they identify must be carried out.
How rare are failures?
Dam failures that flood homes are extremely rare in the UK, and the regulation that exists today was introduced largely because of historic failures. Incidents still happen – in 2019 part of the spillway at Toddbrook Reservoir above Whaley Bridge in Derbyshire was damaged and the town was evacuated as a precaution – but the dam held and the water was lowered safely.
Should you worry?
For most homes, reservoir risk is a very small risk that’s well managed. It rarely affects insurance or mortgages on its own. If your home is in a reservoir flood area, it’s worth knowing the local emergency plan – your council’s emergency planning pages will have it – and signing up for flood warnings in case you need to act.
A reservoir flood area is a worst-case emergency map, not a forecast. Rivers, the sea and surface water are much more likely to matter.
Last reviewed November 2026. This guide is general information about England, not legal, financial or insurance advice. Check the Environment Agency’s own services and speak to a professional before making decisions about a specific property.
