Yes, and more than its hillside reputation suggests. Most of Purley is on dry chalk slopes. A minority of homes, concentrated along the valley, are at high risk. The modelled defences make no difference to how many. The Bourne runs underground through the middle of town, and water has never paid much attention to where it was put.
On the Environment Agency's river-and-sea flood zones, 6% of Purley's postcodes are in Flood Zone 3, the highest-probability band, and about 2% are in Flood Zone 2, the medium-probability band outside it. Zone 2 is the smaller number because the two bands don't overlap, and most of the land the Bourne could reach is already inside Zone 3. That is a small share of the town, and almost all of it follows one narrow valley.
Surface water is the other half of the picture. The Bourne is culverted through Purley and can still flood in the Purley valley, so any rain the culvert cannot carry ends up on the roads above it. The Environment Agency maps surface water separately from rivers and sea, and that measure is folded into the postcode figures further down.
With the Environment Agency's climate allowance added, the share of postcodes in the flood zones goes up to about 9%. That is the agency's modelled view of where the zones could reach once rainfall and river flows are allowed for in a warmer climate, and the extra land is mostly an extension of the same valley.
For insurance, a home in the high-risk band will usually cost more to cover, and some insurers will ask more questions or limit what they offer. Homes on the slopes above the valley should find cover easy to arrange. Get an indicative quote for the exact address early in the process, because what the insurer says will tell you more than any town-wide share.
The wider postcode measure counts a postcode if it is rated on any of several flood indicators, surface water included. On that basis, 18% of Purley's postcodes have a high rating on at least one, 15% a medium rating and 27% a low rating. More postcodes show up here than in the river-and-sea zones because surface water reaches places the Bourne doesn't.
In terms of buildings, the Environment Agency's rivers-and-sea mapping lists 2,346 properties in Purley, and only postcodes with some risk appear on that list at all. Of those, 982 are at high risk, 245 at medium risk, 306 at low risk and 22 at very low risk. The high-risk group includes 825 homes. Most buyers will never be near them, but anyone house-hunting along the valley will be.
On the Environment Agency's modelled flood extents, about 6% of postcodes fall in the high-risk area without defences and the same 6% with defences included. Putting the defences into the model doesn't move the number at all. Whatever protection is in place locally, the agency's high-risk map comes out the same without it.
The nearest tide gauge is at Portsmouth, where the sea has risen by about 2 millimetres a year over the record from 1962 to 2023. That is the rate measured at that gauge over those years. For a London suburb on the North Downs it is background reading, and nobody in Purley is waiting on the tide.
No historic flooding is recorded in Purley's postcodes. That is reassuring, but a missing record does not prove no water has ever come up through a valley road, and the Bourne's culvert exists for a reason.
Flood risk is the place where Purley falls below par. It is a minority problem, but a serious one for the homes it affects, and the defences in the model don't reduce it.