Yes, and most of the risk comes from rain, not rivers. Hardly any of the town is in the river flood zones. About a fifth of postcodes are rated high on at least one flood measure. The last river flood on record was well over seventy years ago. If you judge Walthamstow only by its flood-zone map, the risk looks smaller than it is.
The Environment Agency's river-and-sea flood zones cover a small part of Walthamstow. About 1% of the area's postcodes are in Zone 3, the highest-probability band. Another 3% are in Zone 2, the medium-probability band just outside it. The two figures don't overlap, so between them they cover the whole of the river-and-sea zone footprint here.
Surface water is a different problem. It is rain that drains, gutters and back gardens cannot carry away fast enough, and the river maps don't count it. The Environment Agency has recorded six floods in Walthamstow. The latest was in December 1947, when a main river overflowed a channel too small for it and with no raised defences. Walthamstow's history shows where the water went. The High Street used to be called Marsh Street and led out to the marshes.
The Environment Agency also models the zones with an allowance for climate change. On that version, about 7% of postcodes fall in the river-and-sea flood zones. That is the agency's planning assumption for a wetter future, not a record of anything that has happened.
Insurers rate each address on their own mapping, and that mapping includes surface water. A house well outside the river zones can still get a higher quote. The quickest check is to put the exact address into the Environment Agency's long-term flood risk service, then get a buildings insurance quote while the survey is still being booked.
Counted another way, each postcode gets a rating on several flood measures at once, surface water included, and is flagged at the worst level on any of them. On that count, about 21% of Walthamstow's postcodes are high on at least one measure, about 26% are medium and about 49% are low. "Outside the flood zone" is accurate for most streets here. It just doesn't cover rain.
The Environment Agency's rivers-and-sea mapping also counts individual properties. In Walthamstow, 496 properties are at high risk, 615 at medium, 1,440 at low and 535 at very low, out of 4,832 listed. Of the high-risk properties, 468 are homes. Only postcodes with some river or sea risk appear in that list at all, so a street missing from it has no risk from rivers or the sea. It may still have surface-water risk. A count of 468 homes is small and specific. What matters to a buyer is whether the house they are viewing is one of them.
The agency's flood-extent model can also be run with and without defences. Left out, defences would leave about 1% of postcodes in the high-probability flood extent. With them in the model, the share is still about 1%. "Defended" only means a defence appears in the model. It doesn't mean the house behind it stays dry. In Walthamstow, adding the defences barely changes the map.
The nearest tide gauge with a long record is at Portsmouth. Between 1962 and 2023 it measured sea level rising by about 2 millimetres a year. That the nearest long-running gauge is on the south coast tells you how far Walthamstow is from the sea.
Flood risk is one of Walthamstow's weaker points, and the reason is surface water, not the river. The flood-zone map makes the town look safer than the drains do.