The GMB union said shareholders had “pocketed eye-watering sums” from the privatised water industry, which it called an “abject failure”, including a further £1.4 billion in the form of interest on loans.

Industry returns are in the spotlight after Labour vowed to renationalise the industry and after Southern Water was fined a record £126 million in penalties last week after systematically covering up sewage leaks over seven years.

There are 17 water companies in England and Wales. Three are listed — Severn Trent, United Utilities and South West Water, part of Pennon Group — and the rest privately owned.

The GMB analysis calculates £4.7 billion in dividends were paid out to shareholders between 2014 and 2018, including more than £800 million last year. It counted a further £264 million in other payouts such as share buybacks. It said owners of the water companies had also received £1.4 billion in interest on loans and had accrued a further £520 million in interest, giving a total of almost £6.9 billion it said shareholders had made.

Tim Roache, general secretary of the GMB, said: “If you needed a poster child for abject failure, the privatisation of the water industry is it. Bills up 40 per cent above inflation, billions of litres of water lost in leaks as families face hose-pipe bans and all the while shareholders are trousering billions in profit.”

A spokesman for Water UK, the industry’s representative body, said: “Privatisation of the water and sewerage industry has achieved a great deal over the last 30 years — nearly £160 billion of investment, a healthier environment, better water quality and improved service to customers.

“Customers are now five times less likely to suffer from supply interruptions, eight times less likely to suffer from sewer flooding and 100 times less likely to have low water pressure than when the industry was in government hands. Nationalisation would risk turning back the clock to the days when service and quality failures were far more common, and cash-strapped governments wouldn’t pay for the improvements needed.”