Severn Trent issued a warning in Derbyshire and Leicestershire on Friday after it found high levels of the chemical at a reservoir.
About 3,700 properties are affected in postcode areas DE11, DE15, DE65, DE73 and LE65.
It is hoped the water will be safe to use later, although the firm said customers can now flush their toilets.
Latest updates: Severn Trent Water problems
Severn Trent has been handing out free bottles of water to affected customers at Sainsbury's in Swadlincote, Derbyshire, and Tesco in Ashby-de-la-Zouch, Leicestershire.
Nigel Thornylowe, who lives in Woodville with his two children, said it was a "nightmare".
"We got caught up in the frenzy yesterday and unfortunately... we haven't got any bottled water," he said.
"We've tried in vain but all the supermarkets have run out."
He said the situation had been poorly managed and bottles of water should be distributed at more locations than just the two supermarkets.
But other residents have been looking out for their neighbours with one couple filling up the water carrier in their caravan and distributing it to elderly neighbours.
And another woman said she coped on Friday night by "drinking spritzers" instead of water.
In a statement, the firm tried to reassure customers who may have drunk the water that, if they did not notice a strong chlorine smell or taste, then it was "unlikely to have caused any harm".
But it added that anyone with concerns should speak to a doctor.
"We're very sorry for the inconvenience this has caused but we want to reassure customers that this is a precautionary measure due to the levels of chlorine in the water supply," it said.

The military is the last Turkish institution to see the ban removed. It has long been seen as the guardian of Turkey's secular constitution.
Wearing headscarves in public institutions was banned in the 1980s.
But Turkey's Islamist-leaning President, Recep Tayyip Erdogan, argues that the ban is an illiberal vestige of the past.
The issue has been controversial in Turkey for many years.
Secularists regard the headscarf as a symbol of religious conservatism and have accused President Erdogan of pushing an Islamist agenda, converting many public schools into religious ones as part of his pledge to raise "a pious generation".
Over the past decade the ban has been removed for schools, universities, the civil service and in August for the police.
The BBC's Mark Lowen, in Istanbul, says the secular side of Turkey now feels largely ostracised, accusing Mr Erdogan of governing just for his conservative, religious support base.
The conservatives respond that they were long seen as second-class citizens and the headscarf is an expression of individual liberties.
Our correspondent says that Turkey's religious-secular divide is as old as the republic itself, but is now arguably deeper than ever.
Witness: Turkey's headscarf row
The new rules apply to regular women military officers, non-commissioned officers and female cadets. They will be allowed to wear a headscarf under their caps or berets as long as they are the same colour as their uniforms and are not patterned, Hurriyet Daily News reported.
The military's opposition to the government's move has been weakened after President Erdogan's supporters increased their authority over the armed forces following the failed 15 July coup last year.
The changes will come into effect once they are published in the official gazette.
Turkey has had a secular constitution with no state religion since 1920.
Most people in Turkey are Sunni Muslims.
Thousands of people are still being told they should not use their water because of high levels of chlorine.
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A ban on female army officers in Turkey wearing the Muslim headscarf has been lifted by the government.