Flood Zone 1 is the lowest of the Environment Agency’s flood zones. It covers land with less than a 0.1% (1 in 1,000) chance of flooding from rivers or the sea in any year. Most of England – and most homes – are in Zone 1.
So if your home is in Zone 1, flooding from rivers and the sea is unlikely. But that isn’t the same as saying the home can’t flood.
What Zone 1 doesn’t cover
Flood zones only map rivers and the sea. A Zone 1 property can still flood from:
- Surface water – heavy rain that can’t drain away fast enough. It’s the most common kind of flooding in England and can happen far from any river. See What is surface water flooding?
- Groundwater – water rising through the ground after long wet spells, mainly in chalk areas. See groundwater flooding explained.
- Sewers and drains – overloaded or blocked sewers backing up into homes.
- Reservoirs – very unlikely, but mapped separately. See reservoir flood risk.
How to check the rest
The government’s long-term flood risk service shows surface water and reservoir risk for an address, and whether groundwater flooding is possible in the area. Look at the street as well as the house: homes at the bottom of a slope, in a dip, or with basements are the ones surface water tends to find.
It’s also worth asking the seller whether the property has ever flooded, from any source.
Planning in Zone 1
Most small developments in Zone 1 don’t need a flood risk assessment. One is needed for sites of 1 hectare or more, and for smaller sites in areas the Environment Agency has told the council have critical drainage problems, or where other flood risks have been identified.
Zone 1 is good news for river and sea flooding. Spend two minutes checking surface water too and you’ll have the fuller picture.
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.
