Large holes being dug across the district will help reduce pollution in Bradford's becks.

The scheme, to improve Bradford's combined sewer overflows and costing £17.5 million, includes creating tanks to store heavy rainfall to prevent it from flooding sewage into streams too often.

Water stored in these 50-metre-long tanks can be released slowly through the normal system once the rain abates.

And many current overflows are being fitted with special screens, like this one in an overflow under the Yorkshire Water car park on George Street, which will stop solid waste and "toilet-related matter", passing through into rivers.

If the sewage, heavily diluted by rainwater, was not given this safety valve during times of storm, it would shoot back up domestic toilets and sinks.

Project manager Steve Cooper said: "We are putting in 13,000m of underground storage and improving 50 sewer overflows in the district.

"This will improve the quality of becks in Bradford. At the moment, every time it rains, the sewers overflow into water courses, polluting them to a certain extent."

This project, part of Yorkshire Water's £100 million investment in Bradford, will be finished by April 2004.

At Bradford's main water treatment works at Esholt, state-of-the-art equipment has just been fixed into the system to measure the exact flow of sewage, the first of its kind in the country.

The electro-magnetic flow monitor was sensitively calibrated off-site before being fitted in and is much more accurate than the old system of measuring the height of the effluent on the walls.

New screens have recently been fitted on to the in-coming sewer which sieve out all the paper waste put down toilets or sinks.

Paul Blackburn, operations supervisor, and his team deal with the equivalent of waste from 710,000 people at the Victorian works each day.

In dry weather conditions, 3,000 litres of muck per second flows into the plant, mostly by gravity, but some is pumped from Shipley and Baildon.

It is channelled into holding tanks, where the sludge settles at the bottom and is eventually dried off and burned. The remaining water goes through a filter system and emerges clean enough to flow into rivers.

"This water now is cleaner than much of the water already in the rivers," said Mr Blackburn. "It takes between eight and ten hours to go through the whole process.

"But we would ask people to be aware of what they flush down the loo and put in their sinks."

The 360-acre Esholt plant is as eco-friendly as possible, converting sieved-off bacteria or humus into compost and using heat generated from the solid waste to power a conference and training centre. Trees, flowers, birds and even cows flourish there.

Yorkshire Water workers are cleaning Bradford's ring mains water pipes at the rate of about 1km per week.

With a total of 110km left to do, the £15 million project, which began in April, is not due to finish until December 2005.

The work, part of the water company's £100 million investment to improve water quality, is causing major headaches for motorists, but water bosses say that it is essential.

The 125km-long ring mains is more than 100 years old and carries drinking water around the city to a network of smaller pipes.

Sediment has built up in the pipes over the years which needs removing and contractors are lining old pipes so they stay clean.

Terry Thompson, Bradford Intermediate Ring Mains project manager, said: "We have done about 12km so far, but they were the most difficult.

"This is not an easy job because the trunk mains are built of thick metal. We have to shut each section of pipe off, drain it down, dig a hole at each end, then put the cleaning equipment through it.

"The sediment is sucked out and taken to a waste disposal site.

"Then the pipes are reconnected to the system and refilled with water."

Contractors are working round the ring mains, which vaguely follows the Bradford Ring Road, in an anti-clockwise direction.

At Rooley Lane and Mayo Avenue, which leads to the M606 where closed lanes are currently causing tailbacks at rush hour, there are three mains underground.

Mr Thompson said: "The bad news here is that these pipes were put in more than 100 years ago when this road was a lane used by horse and cart, so they weave about.

"We are doing the best we can, but we have inherited this system and have to deal with it.

"It is a massive project, with big holes, big pipes, big machines and big disruption. But we don't have a choice."

There are dozens of projects to clean the smaller pipes running concurrently to the ring mains project, costing between £2 million and £5 million each.

Q: Why can water be discoloured for some residents while workers are cleaning the pipes?

A: Each section of pipe has to be isolated and water is diverted to customers along a different mains. Because that will increase the flow in the second mains, sediment can be disturbed, so sometimes water will be discoloured.

Q: What is the sediment? Is it dangerous?

A: It is principally iron or manganese, small amounts are present in all water mains throughout the world. The manganese comes from the upland reaches of the peaks.

Q: How can customers find out where roadworks are being carried out?

A: There are weekly updates on roadworks and possible water discolouration in the Telegraph & Argus.

Q: Why are workers lining some of the older pipes?

A: Mains pipes without lining are being sprayed with very quick-drying polyurethane paint which gives a smooth finish. Water will flow faster and improve pressure.

Q: Why are some roads being opened more than once?

A: Some roads, such as Allerton Road, have two mains running underneath them. Workers cannot do both at once because while they are working on one, water has to flow down the other to supply customers.