British Waterways, which runs the nation's 2,000-mile canal network, says capital costs of installing pumps for uphill stretches and building by-passes to avoid working locks and bridges would still run to hundreds of millions of pounds. But operating costs for a network that relied largely on gravity to shift water could be as little as one-seventh of those for a pipeline grid.
A canal grid should also take only five years to implement, rather than 20. Canals already carry about 236 million gallons a day to customers, of which almost two-thirds enters the public water supply via six water companies.
British Waterways estimates that a proposed initial phase could supply an extra 80 million gallons per day to the dry southern and eastern parts of the UK from the wetter North-west. This is a 50 per cent increase on current supplies, and includes an estimated 20 million gallons a day to regions around the river Great Ouse and river Nene - the entire daily demand of those areas.
But Ian Valder, British Waterways' commercial director, warned: 'This is not going to solve the drought problem of the South, it is only part of helping to solve that.'
The first-phase plans for a 162- mile route starting by pumping water into canals north of Stoke- on-Trent in the Midlands, using gravity downhill to Tamworth then pumping up to Braunston near Rugby and down again into rivers near Milton Keynes and Oxford. 'Canals form a link between all these catchments, but where water would not flow naturally,' John Taylor, the water development manager, said yesterday.
British Waterways' directors are seeking consultants to conduct a study into how such a scheme might work. The main missing link is where the extra water would come from. The most likely sources are the mid-Cambrian area, the Kielder reservoir in Northumberland and the river Trent in central England.
It is also unclear who would pay for the cost of upgrading the canal links. Mr Taylor said British Waterways already faced a bill of pounds 68m for a backlog of engineering projects, but added that the privatised water companies were keen to buy more water transported in that way. Some may want to build extra reservoirs to store emergency water, others might decide to turn to the canals as an instantaneous top-up.
The plan aims to preserve the traditional image of Britain's canals as both freight carriers and tranquil waterways for fishing and other leisure pursuits.
Pushing more water through canals dredged to make them deeper, but not wider, would lead to a better environment for today's canal customers, British Waterways argued yesterday.
The organisation also said it would consider possible environmental effects carefully, using submersible pumps that sat below ground.
Mr Taylor said he had already discussed possible water sources for the canal grid scheme with the National Rivers Authority, which is reviewing Britain's water resources and how best to develop them.
Options being considered include expensive schemes for de- salination of sea water, supply from France by pipeline or ship, and extensions of existing water- transfer schemes between rivers. The authority anticipates publishing an interim document on its plans by the end of this year, and a full report by the end of 1993.