NORTH-WEST water firm United Utilities has the dirtiest water in England and Wales.

New statistics from the water watchdog reveal UU fails more quality tests than any other provider.

The Drinking Water Inspectorate says UU’s main problem is producing dirty, orange-brown water because of old iron pipes.

The company has a 99.91% pass rate.

Meanwhile, Thames Water – which is at the top of the league – pass 99.99%.

Principal inspector Sue Pennison said “iron failures” were a particular problem for UU.

She added: “There have been a few of these this year. That’s a factor of the North West being industrial and having Victorian heritage.”

But she said work was ongoing to replace the old pipes and eliminate the issue.

Complaints from consumers about dirty water have fallen by a fifth.

UU said last night it was at the bottom of the table because of changes to how the statistics are compiled.

A spokeswoman also claimed measurements for “concessionary water supplies” unfairly dragged down their figures. These are pipes laid to compensate rural landowners whose natural water supply was disrupted by a water company laying its mains. Rather than using a brook or well to get water, they are fed by the concessionary pipes.

There are around 240 of such supplies in UU’s patch.

But Mrs Pennison said this should not be used as an excuse. She added: “That doesn’t wash with us really.

“They are encouraged to manage these customers as they would any other and have them appropriately treated facilities.”

Frank White, UU’s chief scientist, said: “Drinking water in the North West is the best it has ever been, with 99.9% of all samples meeting tough regulatory standards.

“We are very pleased that the number of customer complaints about water quality has fallen by 20%. This is a direct result of the work we are doing to clean and refurbish our largest water mains.

“Between 2005 and 2010, we are investing more than £1bn on drinking water projects, including schemes to improve supplies from 50 water treatment works and replacing around 2,500 km of old Victorian pipes.”