SOUTHERN Water is "lagging behind" other water companies, according to a new survey by the national water watchdog.

This comes as Ofwat announces that water companies will be forced to repay customers £158m through lower bills for failing to meet performance targets.

The regulator graded the country’s water companies into three categories: “leading”, “average” and “lagging behind”.

While none of the UK's seventeen water companies were awarded the highest “leading” category, three of them, including Southern Water were considered by the regulator to be “lagging behind”.

READ MORE: Southern Water to hold consultation on water plans

Geoff Cooper has described the findings as "disappointing and frustrating" (Image: Supplied) Liberal Democrat parliamentary spokesperson for Romsey and Southampton North, Geoff Cooper has described the regulator's findings as “disappointing and frustrating.”

Mr Cooper is part of the Houghton-based Pan Parish River Pollution Forum, which includes Riverkeepers, members of the Test & Itchen Association, anglers’ groups, local councillors and residents from parishes along the River Test.

The Forum is focused on the protection and preservation of local rivers and waterways from all forms of pollution, and has been pushing Southern Water to do more to prevent ongoing damage to rare local chalk streams like the River Test.

Southern Water will now be forced to pay back £31.9m to customers. However, this is dwarfed by the hundreds of millions more expected to be paid by their 2.5million customers, as the average bill increases from £420 to £603 per a year by 2030. These increases were approved by Ofwat earlier this year.

Southern Water has been criticised by riverkeepers, environmental groups, local politicians and celebrities for persistent issues with sewage dumping, leaks and loss of service in recent years.

SEE ALSO: Danny Chambers MP challenges Southern Water with a walk of the Itchen

Commenting on Ofwats’ report on Southern Water, Mr Cooper said, “It is disappointing and frustrating to see Southern Water is still ‘lagging behind’ other water companies and that the regulator has given them the lowest scoring yet again this year.

“Since the protests last year, Southern Water has been willing to engage but it is evident that progress is too slow and they are not keeping pace with the other water companies, four of which have managed to pull themselves up from ‘lagging behind’ to ‘average’.”

Stuart Ledger, Southern Water’s chief financial officer, said: "This report is a reflection of the first year of our Turnaround Plan, which stabilised and improved our performance in nine of the twelve areas of focus. This included driving down overall pollution, cutting customer complaints and boosting water quality, among other successes.

“There’s further work to be done, but having spent £3bn since 2020, we are preparing to invest billions more over the next five years – to upgrade our network and meet our customers' expectations.”