Hounslow's flood risk falls from the sky. None of the town is in a river or sea flood zone. About one postcode in ten still carries a high rating on at least one flood measure. There's no recorded flood in the area. The rivers can wait. The drains can't.
The Environment Agency's river-and-sea mapping puts 0% of the area's postcodes in flood zone 3, the highest-probability band, and 0% in flood zone 2, the medium-probability fringe beyond it. The River Crane forms part of the town's old western boundary. On the Environment Agency's map, that's all it does to Hounslow.
Surface water is a different matter. It's the flooding that comes when heavy rain falls faster than the ground and the drains can take it away. In a town built this densely, with roads, roofs and paving over most of the ground, the rain has fewer places to soak in. That risk doesn't appear in the river-and-sea zones at all, and it's the reason the town's postcodes show any flood rating.
The Environment Agency's climate-adjusted flood zone, which allows for heavier rivers in future, also covers 0% of the area's postcodes. The river picture for the coming decades looks the same as it does now.
For insurance, a home outside the river-and-sea zones usually starts from a better position. Insurers price by address, though, and a property on a street with a high surface-water rating can still see that in the premium or the terms. Get a quote on the exact address early. A higher premium tells you something no survey will.
The postcode-level measure folds surface water in alongside rivers and sea. On it, about 11% of Hounslow's postcodes rate high on at least one measure, about 20% medium and about 47% low. Those bands overlap with each other, and with the river-and-sea zones above, so they can't be added together. Put the exact address into the Environment Agency's long-term flood-risk service and look at the surface-water layer in particular, because that's where Hounslow's rating comes from.
On the Environment Agency's modelled flood extents, 0% of the area's postcodes are in a high-risk river or sea extent without defences, and 0% are in one with defences. The low-risk undefended share is also 0%. In the model, a defence just means a structure is present, and it says nothing about whether a house stays dry. In Hounslow the question doesn't arise, because the model finds no river or sea water to defend against.
The nearest tide gauge to Hounslow is at Portsmouth. It recorded sea level rising at about 2 millimetres a year between 1962 and 2023. That's the rate measured at that gauge over those years, and Hounslow is far enough inland that a sea-level gauge on the south coast is the nearest one.
No historic flooding is recorded in the area, with 0% of it on the Environment Agency's record of past flood outlines. A clean record helps, though it only covers floods somebody mapped. A flash flood in a back street is the kind of event that can go unrecorded.
On flooding, Hounslow is middling. Rivers and the sea are no threat to it, and the risk that remains comes down to how individual streets cope with a heavy downpour.