THE quality of Cheshire and Merseyside's drinking water is set to be safeguarded for generations in a £350m scheme.

Three water mains serving 3.2m people in the area will be cleaned from end to end for the first time under the eight-year programme - the largest of its kind in Europe.

United Utilities will also carry out repairs on the mains at the River Dee, Lake Vyrnwy in North Wales and Rivington in Lancashire.

The move comes after the company, which supplies water across the North West, announced a 21% increase in profits to £481m last year.

Programme manager, Alan Duncan, said: 'The scale of this job is enormous - our customers have never seen anything like this before, and it's a first for the water industry in this country.'

He added: 'Overall water quality in the North West is the best it's ever been, What we are doing with this job is ensuring that quality is maintained between our treatment works and our customers' taps.'

He said that naturally occurring sediments can settle and collect in water mains over time and the build-up can affect water quality.

'If these sediments get stirred up because of changes in the water flows through the pipe, customers notice that the colour changes in their tap water and they quite rightly complain.

'As well as reducing the risk of this discolouration, which customers can see, the upgrade will help improve water at the microscopic level, which they can't.'

The Dee water main has operated since the 1960s and supplies up to 369m litres of water a day to more than 1.7m customers in parts of Cheshire and Merseyside. The work is due to start in 2007 and should be completed in January, 2010.

The Vyrnwy main takes treated water from Oswestry water treatment works to parts of Cheshire and Merseyside. It stretches 80km and supplies more than 900,000 customers. Cleaning is due to start in 2010, with completion scheduled for March, 2013.

Under the programme, six major water mains across the region will be cleaned.