Different types of flooding have impacted the UK so far in 2026. We have seen fluvial – or river – flooding, which is when rivers or streams burst their banks and flood surrounding areas. There has also been pluvial – or surface water – flooding, which is a direct result of intense or prolonged rainfall that overwhelms drainage systems.

However, a third type of flooding – groundwater flooding – has also been a widespread problem, especially in parts of southern England. Low lying river valleys and areas on chalk aquifers – such as the Salisbury Plains – are most prone to groundwater flooding.

The Environment Agency says groundwater flooding, external occurs when water under the ground (the water table) rises to the surface. This can lead to water filtering upwards above roads or into cellars and basements.

Unlike fluvial or pluvial flooding that tends to improve relatively quickly, the British Geological Survey, external (BGS) says: “Groundwater flooding tends to remain around for weeks or even months at a time, and so causes greater damage to properties.”

Infrastructure below the natural ground level such as tunnels, roads and railway cuttings can be particularly badly affected by groundwater flooding, and the BGS also says “Flooded septic tanks and sewers may mean toilets can’t be flushed”.

In Wales, Scotland and Northern Ireland groundwater flooding is often less extensive than in England due to the bedrock geology and topography. The vast majority of water supplied in Wales comes from rivers and reservoirs, which are currently at more than 90% capacity across the country.

The Scottish Environment Protection Agency (SEPA) warns that high groundwater levels, external could potentially “contribute to the extent and duration of other sources of flooding such as river or surface water flooding”.