Does GU21 flood?

Yes — parts of the GU21 district carry real flood risk: 3 of its 7 at-risk postcodes reach the Environment Agency's High likelihood band. The GU21 postcode district covers Horsell, Knaphill, Bisley & West End, Heathlands, close to Chobham, Mayford, Old Woking, and surrounding villages in parts of Surrey and Hampshire.

7 postcodes in the GU21 district appear in the Environment Agency's rivers-and-sea flood-risk dataset — worst bands: 3 high, 4 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 GU21 postcodes are at risk?

GU21 4XS up to High GU21 4XX up to High GU21 4YH up to High GU21 2RP up to Low GU21 2SJ up to Low GU21 4YB up to Low GU21 8XP up to Low

Rivers and flooding history near GU21

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

Grants Bridge on the Addlestone Bourne — 2.2 km away, highest on record 2.50m
Millbourne Bridge on the Mill Bourne — 2.6 km away, highest on record 2.73m
Woking South on the Hoe Stream — 3.8 km away, highest on record 2.22m
Old Woking on the River Wey — 4.4 km away, highest on record 3.94m

251 official flood warnings and alerts have been raised within ~10 km of the district's centre since 2006 (29 at warning level or above), most recently 14 March 2026. Warnings cover flood areas, not individual addresses.

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

August 2006 flooding — about 3.3 km from the centre
06JanuaryNewYear2003 (2002) — about 3.2 km from the centre

🏠 Buying or renting in GU21? 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

GU20 GU22 GU19 GU23 GU18 GU24 GU17 GU25

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.