The proposal is aimed at curbing the rising demand for water and avoiding the need for costly new reservoirs and pipelines, which all consumers would end up paying for.
The Liberal Democrats' spokesman, Matthew Taylor, said meters would be ''tough but fair''. Every home with a meter would be entitled to a low- payment rate for normal household use, but a higher rate for water consumption above that.
It will be the least popular policy in a populist document built on public antipathy to the water companies' big profits and the large, fast-growing salaries of their senior executives.
Half of profits above those ''expected from an average, low-risk enterprise'' would have to be given back to customers as bill rebates. Alternatively, half the excess profit would be used to cut pollution, or spent on other local environmental projects related to water.
The Liberal Democrats say the industry regulator ought to decide what profits are reasonable. They reject Labour's ''windfall tax'' on utility profits. But the new policy includes a 2-per-cent levy on all water profits to provide grants and interest-free loans for installing water-efficient appliances.
The companies would be set mandatory targets for cutting mains leakage, with financial penalties for missing them.
The document says water bills ought to be cut, by insisting that the companies raise more of the massive investment funds needed for renewing mains and cutting sewage pollution through long-term borrowing and share issues, and less through increased charges to customers.
It would become illegal to disconnect households on low incomes which fell behind with their bills. The charging system applied to most households, which is based on the old council rates, would be replaced by bills based on council tax bands.
Liberal Democrats are keen to see bills cut in the West Country, where they have some of their strongest support, because water there costs more than anywhere else. The reason is the huge cost of cleaning sewage discharged into the sea at hundreds of points along the region's coastline.
The party believes that this coastline, which is Britain's favourite beach area, is a national asset and the cleaning cost ought not to fall only on locals. This and other projects ''of national environmental importance'' would be subsidised by consumers across Britain.Reuse content