Previously, in Marcic v Thames Water, the House of Lords denied the existence of a duty of care by water companies to a private landowner for flooding caused by inadequate sewers.

This principle was considered by the High Court in Oldcorn – Southern Water. A property 75 meters from the sea wall suffered surface water flooding in 2012. A ditch and oversized pipe belonging to Southern are located on the western boundary of the property to deal with run-off water at high tide.

Following a flood in 2009 Southern had installed a valve in its pipe with the intention of preventing further incursion by the sea but the valve also had the effect of restricting surface water discharge at low tide.

In June 2012, following heavy rainfall, the property flooded again and the Claimant believed the new valve was responsible.

Southern relied on Marcic to deny the existence of a duty of care but the Court held that Marcic did not help it as Southern had carried out a positive act in installing a new valve. The valve had the effect of restricting the flow of water in the pipe but this risk had not been assessed by Southern.

The Court found that Southern owed a duty of care in negligence and nuisance. However, whilst the Claimant succeeded on duty and breach of duty, it ultimately lost on causation. Due to issues in the expert evidence, such as the extent of the rainfall, the Court held that the flooding was not, on the balance of probabilities, caused by the installation of the valve.

This decision clarifies and widens the extent of the duty of care owed by water companies to owners of neighbouring properties but also highlights the complexities surrounding causation in flooding.