Does CM20 flood?

Yes — parts of the CM20 district carry real flood risk: 11 of its 23 at-risk postcodes reach the Environment Agency's High likelihood band. The CM20 postcode district covers Hunsdon, Mark Hall, Netteswell, Little Parndon & Town Centre, close to Harlow, Churchgate Street, Sawbridgeworth, and surrounding villages in parts of Essex and Hertfordshire.

23 postcodes in the CM20 district appear in the Environment Agency's rivers-and-sea flood-risk dataset — worst bands: 11 high, 4 medium, 8 low. A postcode not listed here has no properties in any recorded risk band (which is good news, but never proof it cannot flood).

Free preview first · full report £19

Which CM20 postcodes are at risk?

Rivers and flooding history near CM20

The rivers that matter here, each monitored live on FloodRadar:

Harlow Mill on the River Stort — 2.4 km away, highest on record 2.95m
Pishiobury Brook on the Pishiobury Brook — 2.4 km away, highest on record 2.87m
Harlow, Elizabeth Way on the Canons Brook — 2.4 km away, highest on record 2.15m
Sawbridgeworth on the River Stort — 4.8 km away, highest on record 1.98m

98 official flood warnings and alerts have been raised within ~10 km of the district's centre since 2006 (14 at warning level or above), most recently 16 February 2026. Warnings cover flood areas, not individual addresses.

Recorded flood extents near the district (Environment Agency record):

January 2021 flooding — about 2.4 km from the centre
February 2014 flooding — about 1.6 km from the centre
February 2010 flooding — about 2.4 km from the centre
February 2010 flooding — about 2.4 km from the centre

Records, not floods: no outline on the record is not evidence a place has not flooded.

🏠 Buying or renting in CM20? The full property flood-risk report covers any postcode here — the official likelihood band, every recorded flood nearby with distances, warning history year by year, how the local rivers behave, and an insurance outlook, print-ready for £19. See what's in the report →

Flood risk in nearby postcode districts

CM19 CM21 CM18 CM22 CM17 CM23 CM16 CM24

Band = the worst likelihood band of any property in that postcode (EA Risk of Flooding from Rivers & Sea, defence-adjusted, area-level). Check any postcode in detail — or get the full £19 property report — at the property flood-risk report. © Environment Agency copyright and/or database right 2025. All rights reserved. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown Copyright and Database Rights 2025 OS AC0000807064. This product is produced in part from PAF® and Multiple Residence Data, the copyright in which is owned by Royal Mail Group Limited and/or Royal Mail Group plc. All rights reserved. Licence number AC0000807064.