Pinner has a real flood problem, and most of it comes from rain with nowhere to drain, not from the river. Few homes are in the river flood zones. About a third of postcodes are rated high for flooding on at least one measure. Several hundred properties are rated high or medium risk from the river. The suburb shares its name with the River Pinn, and the river is the smaller part of the problem.
The Environment Agency's river-and-sea flood zones cover very little of Pinner's postcodes, about 5% in Flood Zone 3 and about 3% in Flood Zone 2. These are separate bands. Zone 3 is the highest-probability land, and Zone 2 is the medium-probability strip around it. The Pinn runs diagonally through the middle of the village, and the zones follow it closely.
Surface water is where Pinner's flood risk mostly lies. Heavy rain floods streets and gardens because the drains and the small streams can't take it all. About 4% of postcodes have recorded flooding at some point, and the Environment Agency holds 70 recorded flood events for the area. The most recent, in June 2016, came from an ordinary watercourse that overflowed with no raised defence in the way. In a suburb this built up, a small stream that runs out of room causes more trouble than the main river.
Looking ahead, the Environment Agency's zone that allows for climate change takes in about 8% of postcodes. That is the river-and-sea risk if the higher flows the Agency allows for arrive. The land that floods would grow, and the streets it reaches would mostly be the ones that already do.
Insurers will price that risk house by house. A home on the higher ground towards Pinner Hill and one on the low ground by the Pinn can have the same postcode prefix and get quite different quotes. On a listing they look the same. Get an indicative buildings insurance quote on the exact address early, and look up the Environment Agency's long-term flood risk result for it, including surface water. Those two checks will tell you more about a particular house than any figure for the whole of Pinner.
On the wider postcode measure, about 32% of Pinner's postcodes are rated high on at least one flood indicator, about 31% medium and about 47% low. A postcode counts if any one of several measures applies to it, surface water included. That explains why the figures are so much bigger than the river zones above. The same postcode can appear in more than one band.
Counting individual homes instead of postcodes, the Environment Agency's river-and-sea mapping lists 3,179 properties in postcodes with some risk. Of those, 281 are rated high, 299 medium, 677 low and 83 very low. Postcodes with no river or sea risk at all are left out of that list completely. Of the 281 high-risk properties, 209 are homes.
For flood defences, about 4% of postcodes fall inside the high-risk extent with no defences counted, and about 3% inside it with defences counted. "Defended" only means the Environment Agency's model includes a defence nearby. It says nothing about how well that defence works or whether it would keep water away from a particular house. The 2016 flood came from a channel with no raised defence at all.
The nearest tide gauge in the records is at Portsmouth. It measured sea level rising by about 2 millimetres a year between 1962 and 2023. That is a rate measured on the south coast over those years, and it has almost nothing to do with a suburb in north-west London. Pinner's water comes from the sky and the Pinn.
Flooding is Pinner's weak spot. The river risk is small, but the risk from rain and small watercourses is widespread enough that every purchase should be checked house by house.