Yes, more than its river maps suggest. The Mole floods a narrow strip of town. Surface water and groundwater reach far more postcodes. About one postcode in six rates high on at least one flood measure. The river is the obvious risk, and the ground under the town is the bigger one.
The Environment Agency's river-and-sea mapping puts about 2% of Leatherhead's postcodes in Flood Zone 3, the highest-probability band, and a further 1% in Flood Zone 2, the medium-probability fringe beyond it. Those zones follow the Mole along the west side of the town. The town grew up beside a ford on the Mole, and it was built there because the river was shallow enough to walk across. The Agency holds 19 recorded flood events for the area. The latest was in January 2014, when the main river overtopped a channel with no raised defences. About 2% of postcodes fall within a recorded historic flood outline.
The river zones say nothing about rain with nowhere to go. Leatherhead sits where the chalk of the North Downs dips beneath London Clay, which gives the town a high water table and springs along the boundary between the two. Water that cannot soak into clay runs across it, and water rising through chalk turns up wherever it likes. Neither appears on a flood-zone map.
With climate change built into the model, the Environment Agency's river-and-sea zone share for Leatherhead rises to about 3% of postcodes. That changes the modelled scenario the Agency plans against, and it still covers only the river and sea.
For insurance, a home in Flood Zone 3 or with a recorded flood history will cost more to cover, and some insurers will ask detailed questions or decline. Homes outside the river zones but on a surface-water route can still be priced up, because insurers use their own models, not just the Agency's zones.
Across all measures together, surface water included, about 17% of Leatherhead postcodes rate high on at least one, 18% medium and 27% low. Those bands overlap with the river zones and with each other, so they cannot be added up. With only 2% of postcodes in the highest river zone, most of the high ratings come from measures other than the Mole. Putting the exact address into the Environment Agency's long-term flood risk service, and reading the surface-water result as carefully as the river one, is the one check worth doing here.
Counted by building, the Agency's rivers-and-sea mapping lists 532 properties in the 27 Leatherhead postcodes that carry any river risk at all. Of those, 150 are at high risk, 40 medium, 42 low and 14 very low, and 43 of the high-risk properties are homes. Postcodes with no river risk are left out of the count entirely, which is why it covers so few of the town's homes.
In the Agency's modelled flood extents, about 2% of postcodes are in the high-risk area with no defence in the model, and about 2% where a defence does appear. A defence in the model means a wall or embankment was counted when the water was drawn, and says nothing about whether it will hold. In 2014 the Mole flooded a channel with no raised defences.
The nearest tide gauge is Portsmouth, which recorded sea level rising about 2 millimetres a year between 1962 and 2023. That is the nearest gauge to Leatherhead, and it is a long way off. Sea level is not a Leatherhead problem.
Flooding is one of Leatherhead's weaker points, and the river is the smaller part of it. The clay, the springs and the surface water reach far more postcodes than the Mole does, and a buyer who checks only the river zones has checked the wrong map.