Britain should tackle future droughts by recycling more sewage effluent as drinking water, civil engineers say.
The public have been repeatedly urged to use less water
In its State of the Nation report for 2006, the Institution of Civil Engineers also called for a 20% rise in water prices to fund improved supply.
But Water UK, which represents the water companies, attacked the "sensationalism" in the report.
Pressure group Waterwise said although more effluent use was a possibility, demand management was key.
The south east of England was in the grip of water shortages over the summer, with one company enforcing a drought order controlling use of water and a number of others enforcing hosepipe bans.
The Institution of Civil Engineers' chairman, Gordon Masterton, said there would be a "huge shortfall" in around 20 years "if we do nothing at all about securing our water supplies".
He said this was particularly the case in South East England.
Pipeline from Wales to South East England
20% price rise
As well as increasing use of effluent, ICE said it was time to fund new reservoirs, desalination plants to remove salt from water, and pipelines from wet regions like mid-Wales to the South East.
Water prices rising to match those elsewhere in Europe should be accompanied by compulsory metering in some areas, the report said.
ICE water board chairman John Lawson said: "Effluent water reuse is still a relatively untapped way of providing drinking water to meet growing long-term needs."
Turning effluent into drinking water involves a sieving and chemical cleaning process of waste water so it can be pumped into rivers and then taken back into the water purification process.
But Water UK said it would be wrong to change the current policy on effluent reuse as the industry was already part of a "natural water cycle".
Aerated shower heads
Turn off tap when brushing teeth
Run full washing machine loads
And Jacob Tompkins, director of Waterwise, said water management by consumers was the way forward, with such items as "save-a-flush bags" for toilet cisterns, flow restrictors on taps and aerated shower heads having proved a success in other countries.
Andrew Marsh, of the Consumer Council for Water (CCW), said water companies should concentrate on getting their core services right before considering effluent re-use.
He said: "We would rather water companies focused on other things which need improving, such as repairing the leaky pipes or improving connections between supply networks in the south-east.
"Sewage effluent and reuse is something to look at later if these more basic measures do not do the trick."
The CCW said that since 2003 Essex and Suffolk Water had been recycling treated effluent for drinking water.
The State of the Nation report also tackled other UK infrastructure issues such as energy, where the ICE said it was time to cut consumption and diversify supply.
The engineers also said it was time to view waste as potential resources instead of a landfill problem.
HOW SEWAGE IS RECYCLED
1. Wastewater is pumped into a clarifier
2. After passing through filters it is then disinfected with UV light
3. The water is then pumped into rivers, to be taken back into the water supply later