For most of Bishop's Waltham, flooding is not the thing to lose sleep over. Rivers and the sea barely feature here. The real exposure, where there is any at all, is surface water after heavy rain. About one in ten postcodes carry a higher surface-water risk, and a similar share a medium one. Everywhere else, the flood question is close to a non-issue.
Start with rivers and the sea, because they are the easy part. Only around one in a hundred postcodes fall inside the medium river-and-sea flood zone, and effectively none sit in the highest zone. The town rises at the source of the River Hamble, so the water starts small here rather than arriving in volume from upstream, and the coast is a little over five kilometres away, far enough that tidal flooding is somebody else's problem. The town also carries no mapped history of past flooding, which is a modest comfort but a real one. If your worry is a river bursting its banks or the sea coming in, this is about as quiet as inland Hampshire gets.
Surface water is where the map earns its keep. When rain falls faster than the drains and the ground can take it, water pools in the low spots, and here that reaches a genuine minority of homes. Close to one in ten postcodes carry a higher surface-water risk and a similar number a medium one, while about a quarter show some lower-level risk. That is not a town-wide problem, but it is a street-level one, and the averages will not tell you which side of it your particular house sits on. Check the specific address, not the postcode district, before you fall for the garden.
Looking forward, the climate-adjusted picture nudges the numbers up rather than transforming them. Under three percent of postcodes fall into the flood zone once future climate allowances are folded in, a small creep on today's figure rather than a step change. It is enough to take seriously if you are buying at the wetter end of town, and not enough to rewrite the answer for everyone else.
For insurance, the split matters more than the headline. The large majority of homes here should attract standard flood cover on standard terms, because standard is what the underlying risk is. For the minority in the higher surface-water pockets, cover is generally still available, and the Flood Re scheme sits behind household flood insurance to help keep it that way, though that scheme does not cover homes built since 2009. If you are buying one of the newer builds in a wetter patch, price the insurance before you fall for the kitchen, because that is the corner where a nasty quote is most likely to turn up.
The verdict is a middling three out of five, and it is the honest mark. Rivers and sea are close to a non-event, surface water is a real but contained risk for a slice of the town, and the whole thing comes down to which specific piece of ground you end up buying on.