A little from its rivers, more from heavy rain. Only a small part of the town sits in the river flood zones. Roughly one postcode in eight rates high on at least one flood measure. Several hundred homes sit in the top river-risk band. "It's miles from the sea" is true, and it's no reason to skip the flood search.
In the Environment Agency's river-and-sea flood zones, about 2% of the area's postcodes fall in zone 2 and about 1% in zone 3. The two are separate bands. Zone 3 is the higher-probability land nearest the water, and zone 2 is the medium-probability fringe beyond it, so the fringe doesn't include the core. The rivers in question are the Ray to the west and the Cole to the north-east, with the Thames along the northern edge of the borough. None of it adds up to a river town.
Surface water is where the local flood history sits. The Environment Agency holds 41 recorded flood events for the area, and about 1% of it lies inside historic flood outlines. The most recent recorded event was on 29 July 2007. Its cause was logged as a blocked debris screen: a drainage grille clogged with rubbish, not a river bursting its banks. That kind of flood depends on your particular street and its drains, not on a map of the nearest river, and it is easy to miss when a buyer checks only for water nearby.
With the Environment Agency's allowance for climate change, the share of postcodes in the flood zones grows to about 3%. It is still a small share, but it is bigger than the current zones, and that is the version of the map a 25-year mortgage will run into.
For insurance, a home outside the flood zones on a street with no flood history is usually quoted routinely. A home in zone 3, or on a road with recorded flooding, may cost more to cover, carry a higher excess or be harder to place. Get an indicative quote on the specific address before you instruct a solicitor, not after the survey.
The postcode-level measure is broader because it folds surface water in with rivers. About 13% of postcodes rate high risk on at least one measure, 14% medium and 29% low. These bands overlap with the flood-zone shares above. They measure something different, so don't add them together, and don't read them as the same thing.
Counting homes rather than postcodes, the Environment Agency's rivers-and-sea mapping lists 5,569 properties in postcodes carrying some risk. Of those, 563 are at high risk, 169 at medium, about 1,230 at low and 179 at very low. Only postcodes with some river or sea risk appear in this count at all, so it isn't a share of the whole town. Of the high-risk properties, 510 are homes.
On defences, about 1% of postcodes sit inside the high-risk extent with no defence in the model, and about 1% sit inside it where a defence is modelled. "Defended" means a defence exists in the Environment Agency's model. It doesn't mean the house stays dry. Defences are designed to a standard, and a flood bigger than that standard goes over the top.
The nearest tide gauge is at Portsmouth. It recorded sea level rising at about 2 millimetres a year across its record from 1962 to 2023. That is a measured historic rate on a distant coast, not a forecast, and Swindon is a long way inland from it.
Swindon's flood risk is middling: river flooding is limited to a narrow strip, while surface water can reach streets well away from any river. Check the exact address, its drainage record and its insurance quote, and the town-wide share becomes much less important.