Flood risk in CM18 (Harlow)
Of the 432 postcodes in CM18 – covering Harlow – none has its centre in Flood Zone 2 or 3 on the Environment Agency’s Flood Map for Planning. River and sea flood risk across the district is low.
Flood zones only cover rivers and the sea, and ignore flood defences. Surface water from heavy rain can affect any street, including in Zone 1.
Flood zones by postcode sector
Each sector is the first part of the postcode plus the first digit after the space.
| Sector | Postcodes | Zone 3 | Zone 2 | Breakdown |
|---|---|---|---|---|
| CM18 6 | 229 | 0% | 0% | |
| CM18 7 | 203 | 0% | 0% |
Main rivers in Essex
Thames estuary – Canvey Island, Southend and Thurrock
River Chelmer – Chelmsford and Maldon
River Colne – Colchester and Wivenhoe
More on the area in our Essex flood risk guide.
How these figures are worked out
We took the centre point of every live postcode in CM18 from OS Code-Point Open and tested it against the Environment Agency’s Flood Map for Planning, as published in the flood-risk-zone dataset (version of 5 November 2026). A postcode counts once, whether it has one home or forty, and a postcode whose centre is just outside a zone still counts as Zone 1. Updated November 2026.
For one address, the free postcode check looks at the zones around the postcode, and the full report adds surface water, reservoirs, recorded floods and defences.
