People are being urged to conserve water as some areas suffer problems with supplies because of high demand in the heatwave.
Water companies are calling on customers to put away garden sprinklers, take short showers instead of baths, and avoid using hoses to clean cars or water the plants to reduce demand.
Huge spikes in demand for water at mornings and evening peak times mean utilities are having to pump billions more litres of water into the system, but they say it is often being used by customers as fast as it is supplied.
Customers in some areas may notice a drop in their water pressure, unless people make some simple changes to the way they use water, industry body Water UK warned.
Some parts of Staffordshire and Shropshire have seen supplies temporarily interrupted as a result of high demand, prompting Severn Water to set up bottled water collection points "as a precaution".
It's been a busy night for our tanker crews as they helped keep customers on supply by injecting water directly into our pipes pic.twitter.com/EliJWwDsO9
-- Severn Trent (@stwater) June 28, 2018
Overnight tanker crews also injected water directly into pipes in the region to keep customers supplied with water.
Severn Trent said there was plenty of water in reservoirs, and it had put an extra 300 million litres of water into its pipes on Wednesday, but the network could only carry "so much water".
Doug Clarke, Severn Trent's water efficiency expert, said: "We need people to think about how they're using water - using a sprinkler might green up your lawn but that water would be better used for drinking or washing."
He added: This is all about being neighbourly.
"Just think about whether you're making the absolute best of the drinking water we're producing for you and your neighbours."
We are seeing very high demand for water in this hot weather, particular during peak periods in the morning and evenings. We appreciate our customers' efforts to use less water at this time. Follow our water saving tips here: https://t.co/IPNqvofOx7 ? Chloe
-- Affinity Water (@AffinityWater) June 27, 2018
Customers in some parts of the Home Counties served by Affinity Water have also seen interruptions to supply or low pressure as a result of soaring demand for water in peak periods.
An Affinity Water spokesman said: "We usually supply on average 900 million litres of water each day to 3.6 million people and we have had to significantly increase this to meet demand due to the hot weather.
"This demand is averaging at 1.2 billion litres of water per day, but at times this has peaked to 1.6 billion litres of water in a single day.
"We are asking all customers to use water wisely, to reduce the demand on our network."
The company is urging people to adopt measures such as watering the garden with a watering can, teaming up children with their friends for paddling pool dates to avoid filling up too many pools and to not worry about the lawn going brown.
During the #heatwave, you may notice your water pressure drops due to extra demand for water in the morning and when you get home from work. Our Water Services Director, Martin Padley explains more in this video. Use water wisely https://t.co/tWbgJmjo1j#Heatwaveukpic.twitter.com/YkOVxoricw
-- United Utilities (@unitedutilities) June 28, 2018
Elsewhere people served by Southern Water "may experience low pressure overnight as we refill the network to exceptionally high water demand. This is likely to be ongoing for the next few nights", the company said.
But rain in winter and spring had helped recharge reservoirs and groundwater supplies, so there were unlikely to be any restrictions such as hosepipe bans this summer, Southern Water said.
Despite seeing high demand, other companies were reporting no heatwave-related problems or threat of hosepipe bans, but called on households to conserve water.