THOUSANDS of residents are being advised to boil their tap water to rid it of a foul smell.

Householders are being told that any unpleasant taste or odour in the water is caused by a naturally occurring organic compound and is harmless.

Bristol Water's Jeremy Williams said: "There is no need, for quality reasons, to boil the water before drinking, but it might help remove the taste for those with the most sensitive palates."

The problem, known as geosmin, was discovered two weeks ago in pipes supplying north and east Bristol.

The water firm did not alert at least 200,000 customers potentially affected because it feared an unmanageable number of calls.

Customers found out only when they called the company for advice on how to rid their homes of the noxious smell.

More than 600 complaints about the "earthy smell" have been made from areas including Yate, Keynsham, Filton and Fishponds.

Mr Williams, of Bristol Water, said: "It's something that happens every year, but this year it's worse because there has been so much rain water.

"The source is the River Severn, joined by the Gloucestershire and Sharpness Canal, which delivers the water to Purton Works.

"Tests done at Purton Works on Friday show there is no trace of the material in the water there, so it should clear up in a day or so.

"On Thursday we had 30 calls and Friday 17, so the problem is getting better."

Mr Williams admitted Bristol Water had decided against issuing advice or warnings to its customers after discovering the problem.

He said: "If we put out a notice saying there's a smell, we would get calls from 1.2 million customers.

"We supply half a million homes in Bristol. It's not really affecting the quality of the water."

Brian Jenkins, 81, of Bath Road in Keynsham, said: "I got back from holiday in Scotland on Wednesday and I noticed a really unpleasant taste in the tap water.

"I was cleaning my teeth and there was this lingering foul taste which eventually went away over time. I drank tonic water to try and get rid of it.

"In the morning it was still there so I called Bristol Water and they confirmed there was a problem.

"They told me to boil the water to get rid of the taste, but why didn't they tell people? It's disgraceful. It makes it look like they have something to hide."

Steve Hobbs, policy manager for the regional Consumer Council for Water, said: "We were notified on August 15 when Bristol Water discovered the problem.

"The cause has been the heavy rainfall causing a lot of dead wood to be washed into the river.

"It's depends on the palate of the drinker, just like people don't like chlorine. Although it's harmless, it's unfortunate customers have been affected in this case.

"Bristol Water acted accordingly, but in this instance they were reactive rather than proactive.

"We will be discussing this case with them to prepare for future incidents."

Bristol Water supplies drinking water to 1.2 million customers in a 1,000 square mile area including parts of Gloucestershire, Somerset and Wiltshire. An average water bill in the area is set to rise from £150 to £162 by April.