"We have not seen flooding of this magnitude before," said Anthony Perry, an Environment Agency flood risk official. "The benchmark was 1947 and this has already exceeded it."
Police in Gloucestershire - the worst-hit area - said the peak of the "unprecedented" crisis was "by no means over", with water levels in the River Severn expected to hit their full height tomorrow evening.
Meanwhile Prime Minister Gordon Brown, who today flew over the stricken county by helicopter, announced a Government review of flood infrastructure and more funding for defences and the current rescue operations.
Up to 350,000 homes in the area are likely to lose their water
supply over the next 15 hours after the Mythe Water Treatment Works
in Tewkesbury flooded. Severn Trent Water has already cut off
supplies to 70,000 homes in Gloucester, Cheltenham and Tewkesbury.
It will take at least a week, possibly up to two weeks, before the plant can again supply them with fresh water, Severn Trent Water said. Six hundred water tanks are being drafted in with military help, while 150,000 bottles of water are being handed out at local supermarkets.
The treatment works, which is at the meeting point of the River Avon and the River Severn, has not flooded for 100 years.
More than 48,000 homes across Gloucestershire and neighbouring Herefordshire have also lost their electricity supply after Castlemeads substation in Gloucester was deluged.
About 150 firefighters and servicemen from RAF Innsworth managed to stabilise a second substation at nearby Walham, which serves more than half a million homes, by erecting a metal ring with sandbags around it.
Forecasters warned more rain was on the way, while nine severe
flood warnings remained in place across England - four of them
along the Severn and two along the Thames.
A spokesman of MeteoGroup UK said about 0.8in of rain would fall across Gloucestershire today, compared with the 4.7in which fell on Friday. "It is not particularly heavy rain but it is not going to budge and it will only add to the already high river levels."
The rain should clear slowly overnight, but is expected to return heavily on Wednesday and could cause more problems next weekend.
Elsewhere:
The floods also disrupted rail travel, with scores of services cancelled in the West Country and the Midlands. Rail replacement buses could not run on the flooded roads, and there were long tailbacks on the M5 around Gloucestershire.
Meanwhile the Government's own planning consultants warned
that Mr Brown's proposals to build three million homes in the
South East could lead to even more flooding.
With vast swathes of the country underwater, the Prime Minister's new government found itself under attack not only over its handling of the crisis, but also accused by the Tories of adopting policies that could make things even worse.
The plans for the new houses - a key plank in Mr Brown's strategy - are due to be unveiled today in a Green Paper.