Homes across the UK are facing water supply problems - with thousands of people in Wales and south-east England urged to use as little as possible.
Water suppliers say a thaw has led to burst water mains and leaks.
About 13,000 homes are still without water in Kent and Sussex while thousands of properties in Wales and 5,000 homes in London also have no supply.
The industry regulator Ofwat has said water firms have "fallen well short".
Suppliers across the country say teams are working to fix damaged pipes that have left customers with no supply or low pressure.
Water companies said cracks and splits had been caused by the freeze which are now being exposed as the pipes thaw.
Parts of the Midlands, south-west England and Scotland are also affected.
West Midlands-based carmaker Jaguar Land Rover has agreed to stop production to preserve the water supply for homes, hospitals and schools.
Chocolate maker Cadbury also sent workers home from its Bournville plant but said it was able to continue some limited production.
In south-east England and Birmingham, suppliers say they have been identifying vulnerable customers and providing them with bottled water.
At its peak, more than 20,000 homes in south and north London were left without water on Sunday.
Supplier Thames Water said the number of homes affected was constantly falling and was down to about 5,000 by Monday evening.
The company said it was taking longer than expected to restore supplies to homes in the SW12, SW15 SW16 and SW17 postcodes.
It said households in NW2, NW3, NW5, NW11, N2, N6, N10 and N19 may still be facing low pressure but staff were working in those areas.
The company says it distributed almost a million litres of water across the weekend and was continuing to offer to supplies to households in the affected areas of London.
London Mayor Sadiq Khan said it was "unacceptable" that thousands of homes in the capital still lacked water.
Several schools in London and Kent were closed on Monday because they were unable to guarantee running water.
South East Water set up a number of bottled water stations in Sussex and Kent where 13,000 homes had been affected.
Southern Water, which had urged customers to "only use the water you absolutely must", said it was restoring the supply to 5,000 homes in Sittingbourne, Kent but there were still 900 homes without water in Hastings and interruptions to supplies in the Crawley area.
In Wales, about 3,500 customers are without water, Welsh Water said.
Thousands of customers are also without water in parts of Birmingham, the West Midlands and Staffordshire.
Yorkshire Water, United Utilities, Affinity Water, Anglian Water and Bristol Water also reported problems.
Severn Trent, which said it had seen an increase in reports of burst pipes, thanked Coventry-based carmaker Jaguar Land Rover for agreeing to stop production "to help us target our supply".
South West Water said it has an "unprecedented number of burst water mains" and warned some customers in Devon and Cornwall that, although water can be used, there is a "noticeable taste".
@thameswater, 48 hours without a proper wash now and no clean shirts for work tomorrow! Worst customer services I have experienced in a long time! When do you expect IG7 to have water fully restored!— DJ-M-R-J (@MRJ_DJ) March 4, 2018
There’s no water in north London and Thames water is handing out bottles like it’s a 3rd world country— Cam (@BFooli) March 4, 2018
#thameswater— Paul King (@paulpkking) March 4, 2018
So Thames Water why can't you acknowledge that SW17 has had no water since Saturday night?
The government's water industry regulator Ofwat has released a statement which said a number of water companies had "fallen well short on their forward planning".
Rachel Fletcher, chief executive of Ofwat, said customers had been left "high and dry" because of firms' support and communication.
She said: "Water companies have been warned time and again that they need to be better at planning ahead to deal with these sorts of situations."
Parts of the UK are still recovering from the effects of Storm Emma and the recent freezing weather, with more than 100 schools in Wales still shut due to snow or icy conditions.
In Cumbria, the RAF has been called in to fly food supplies, coal, logs and electrical heating appliances to isolated communities, where many homes have been cut off from all supplies for five days.
And in Scotland, two Met Office yellow warnings for snow, rain and ice remain, with people being urged to travel with caution, while ongoing bad weather has been slowing down water repair works.
In London, customers said the water helpline was unavailable, while shops reportedly ran out of bottled water in some areas.
"We are putting as much extra water as we can into our local networks and fixing leaks and bursts as quickly as possible," Thames Water said in a joint statement with South East Water, Southern Water and Affinity Water.
"Please do not use water for anything that isn't essential. This will make a real difference."
We are doing everything we can by fixing bursts and detecting leaks so that we can help maintain supplies and we will continue working throughout the night.— Welsh Water (@DwrCymru) March 4, 2018
We will continue to prioritise services to vulnerable customers including hospitals and care homes etc.
It's a difficult few days for our customers - and— Southern Water (@SouthernWater) March 5, 2018
for us too. #BigFreeze+#BigThaw=Big Problems. We're very sorry for
the inconvenience. We're working round the clock to put things right. We're getting lots of messages so please checking our web page and social media.
Our teams are still out working hard to fix as many leaks as possible following the rapid thaw we've experienced. If your water is affected, we're really sorry and we're doing everything we can to fix the leaks and get things back to normal as quickly as possible.— Severn Trent (@stwater) March 5, 2018
Temperatures in most places increased over the weekend, however, a Met Office yellow warning for rain and snow in Scotland is in place for Tuesday.