Image description: Red floor tiles under a thin layer of water. Photo by Annie Agarwal on Unsplash

Southern Water has announced an £11 million investment in Hampshire to cut groundwater flooding risk after this winter’s severe wet weather. The programme will include sewer sealing work to prevent groundwater entering the network, alongside resilience measures in at-risk areas where water tables rose above normal during sustained rainfall.

What groundwater flooding means

Groundwater flooding differs from surface or fluvial flooding – occurring when water tables climb above foundation level, forcing water into homes and buildings through walls and floor slabs. It develops slowly, over days or weeks, rather than suddenly, making it harder for residents to predict and recover from. During this winter, parts of Hampshire experienced sustained groundwater emergence as rainfall persisted for weeks.

Traditional flood defences that work against river overtopping are ineffective against rising water tables. Sewer sealing addresses one pathway, by preventing groundwater from forcing its way into the network through cracks or joints in old pipework.

Investment rollout

The investment will roll out in phases over the coming years, with initial work targeted at locations that experienced the greatest impact during winter. Southern Water has indicated that areas where customers experienced internal flooding this winter will be early recipients of sewer sealing work.

The programme will sit alongside flood defence work led by the Environment Agency and Hampshire County Council. Southern Water faces wider pressure on its finances and operational performance; the groundwater initiative represents a near-term commitment to affected residents in its operating region.