Water company bosses have asked the government for urgent help in providing clean supplies to flood-hit Gloucester, amid fears they are running out.
Severn Trent Water says 350,000 people are without tap water and it could be two weeks before supplies are restored.
Many residents say they have struggled to find any mobile street dispensers - known as bowsers - with water in them.
Gordon Brown, who had earlier pledged £46m for flood-hit councils, promised that more water supplies were coming.
Fresh floods have also hit Oxford while areas further along the Thames have been told water levels may peak later.
Homes were evacuated in Oxford overnight while places including Reading, Henley and Caversham are braced for similar flooding.
The Environment Agency still has six severe flood warnings in place - three on the Severn - in Gloucester, Tewkesbury and Worcester - two on the Thames around Oxford, and one on the Ock, near Abingdon, Oxfordshire.
BBC weather forecasters said flood-hit areas would see heavy rain of 10mm to 15mm on Thursday, which could slow the speed at which waters recede.
In Gloucestershire, water supplies were cut off after a treatment plant flooded.
Severn Trent Water is supplying more than 1,000 bowsers, while the Army delivered four million bottles of water on Wednesday.
But Gloucestershire's Chief Constable Tim Brain said there had been instances of people "behaving most selfishly", using "very large receptacles" to empty bowsers and trying to resell water at inflated prices.
"That is simply theft and it is being treated as theft," he said.
A Severn Trent spokesman said they were aiming to do four or five refills per day but that one bowser could be emptied in less than half an hour if people filled up large containers.
Prime Minister Gordon Brown, on his second visit to the region since the floods, said great efforts were being made to help those without water, but added: "We've got to get the supplies stepped up.
"We will get more tankers in, we will get more bowsers in, we will get more regular filling of them, and at the same time, more bottled water will be provided."
He said a government review of the flood crisis and the response to it would look at whether similar problems could be avoided in future.
Mr Brown also told the House of Commons he would push insurance firms to make payouts.
Responding to questions in the Commons, Mr Brown said all councils affected by the floods would receive 100% compensation.
Central Trains - services between Great Malvern and Hereford suspended
First Great Western - services suspended between Oxford and Didcot, and Oxford and Worcester
Virgin trains - services between Oxford and Reading suspended
He said that besides immediate spending, annual funds for flood protection would rise to £800m by 2010/11.
In Gloucestershire long queues formed in supermarket car parks as people waited to collect their daily ration of six two-litre bottles of water.
At Tesco in Quedgeley residents said the crisis had fostered a war-time spirit.
Reginald Davies, 91, who fought during World War II, said: "I did five days without water in Burma.
"I've seen men go mad from thirst. This is nothing."
Severn Trent Water said on Wednesday evening that it hoped to use a temporary solution to restore water supply to 10,000 homes in Tewkesbury from Thursday.
Meanwhile police said Mitchell Taylor, 19, who has not been seen since leaving a bar in Tewkesbury at the height of the floods on Saturday, was still missing.
Environment Agency floodline: 0845 988 1188
SEVERE FLOOD WARNINGS IN PLACE
The Severn: Severe warnings for Gloucester, Tewkesbury and Worcester
The Thames: Severe warnings affecting Eynsham to Sandford Lock and also Little Wittenham
The Ock: Severe warnings from Charney Bassett to Abingdon