United Utilities says most customers will not notice any difference

The �350m scheme to clean the system is being carried out by United Utilities and will take eight years.

The work is being trialled for three weeks from Monday before the cleaning equipment is put into place next year.

The company says most customers will not notice any difference in their supplies, and any discolouration will not affect the quality of the water.

As part of the test, engineers will slow the speed of the water flowing through one main and then speed up the flow of water in another.

Engineers will target sections at a time, using high pressure water jets to remove sediments and deposits that have built up over time.

Alan Duncan, who is leading the clean-up team, said: "These naturally occurring deposits can start to affect water quality and if they get stirred up customers can notice a change in the colour of the water coming out of their taps.

"The water is safe to drink but customers don't like it.

"Our cleaning programme will reduce the risk of this discolouration happening and improve the overall quality of the water into the bargain."