Potters Bar has a flood problem, though rivers and the sea play almost no part in it. Hardly any of the town is in a river flood zone. A quarter of its postcodes still rate high on at least one flood measure. Nothing in the official record shows the town ever having flooded. The risk is real, and it comes by a route most buyers here never think to ask about.
On the Environment Agency's river-and-sea flood zones, about 1% of the area's postcodes are in Flood Zone 3, the highest-probability band, and fewer than 1% are in Flood Zone 2, the medium-probability fringe beyond it. The two bands don't overlap, so the second figure adds to the first. A town on the old Great North Road, with the M25 at one end, has no great river to blame, and the zone map reflects that.
Surface water is a different matter. The Environment Agency maps it separately, and it measures rain that runs off roofs, roads and driveways faster than the ground and the drains can take it. In a town of semis with paved fronts, that water has plenty of hard surface to travel across. The house-by-house surface-water result is on the Environment Agency's long-term flood risk service, and it is the line to read for any address you're serious about, because the river map will tell you almost nothing here.
The Environment Agency's climate-adjusted flood zones, which model the extra water expected in a warmer future, take in about 2% of the area's postcodes. That is a slightly larger slice than today's zones, and still small.
For insurance, a home in a river flood zone or on a high surface-water rating can mean higher premiums or fewer insurers willing to quote, and a home with no rating at all usually goes through without comment. Where a house falls on that line matters more than where the town does.
The postcode-level picture is harsher than the zone map because it counts any of several flood measures, surface water included. On that basis, about 26% of the area's postcodes rate high on at least one measure, about 25% rate medium, and about 50% rate low. A postcode lands in the high group if a single measure puts it there, so this is the widest net on the page.
The Environment Agency's rivers-and-sea mapping counts properties instead of postcodes, and only postcodes carrying some risk are listed at all. Across the 23 postcodes it lists, covering 561 properties, 67 properties are at high risk, 61 of them homes, with 17 at medium risk and 52 at low risk. That is the number of front doors the river model is actually worried about, and it is a short list.
On defences, about 1% of postcodes fall in the high-risk river extent with no defence in the model, and about 1% fall in it with a defence present. A defence in the model means a wall or bank was counted when the map was drawn. It says nothing about whether that defence will hold, and an embankment does nothing about rain falling on the street.
The nearest tide gauge is at Portsmouth, which has recorded sea levels rising by about 2 millimetres a year between 1962 and 2023. That the closest gauge is in Portsmouth tells a buyer most of what they need to know about the sea's interest in Potters Bar.
The flood record holds no historic flooding for any of the area's postcodes. That is good news, and it also only counts what someone wrote down, so a dry history is reassuring and stops short of proof.
Flooding is the soft spot in Potters Bar. The rivers barely figure, but the surface-water and postcode measures flag enough of the town that every serious buyer should look up their own street.