Water customers are preparing for a payout after Thames Water agreed to pay £86m of penalties for misreporting the number of properties at high risk of sewer flooding.

An investigation by Ofwat revealed that between 2005 and 2010 the company claimed more properties were at high flood risk than evidence supported.

The utility firm – which supplies customers in the Dartford area – has agreed to a £79m reduction in the way it sets price limits, which the regulator says will lead to lower bills for its 15m customers.

The company will also give back £7m to customers and the community.

Ofwat chief executive Cathryn Ross said: “We welcome Thames’s co-operative approach which means we have concluded our investigation more quickly and resulted in a better outcome for customers.

“We are satisfied that Thames has put right the problems that caused the misreporting. It’s only fair that when companies make mistakes, they put it right and make sure customers are not out of pocket.”

A Thames Water statement said: “We made a mistake in some of our 2009/10 sewer flooding statistics.

“Ofwat agree that this was not deliberate and we are pleased they have accepted our package of measures in response.

“This is a positive result for our customers, communities and the environment.”