People living in the Bicton Heath area of Shrewsbury said their water had gone off around 6pm on Tuesday, with supply still not restored as of 7.30pm on Wednesday..
Problems were said to be affecting both the SY3 and SY5 areas.
Severn Trent said it believed eight properties had been affected and apologised for the issues – and for the fact no bottled water had been sent to the homes.
The company said it had been "unaware" of the issue, and was "absolutely mortified not to have spotted that earlier".
It comes as Shrewsbury saw temperatures climb as high as 29C on Wednesday with the region under a Met Office 'amber warning' for 'extreme heat'.
One Bicton resident said the situation had been exacerbated by a lack of information about the issue, and when it would be fixed.
They also expressed surprise that Severn Trent had not delivered bottled water or bowsers where people could fill their own bottles – and added that the Bicton Heath Co-op had also sold out of bottled water.
Severn Trent posted a series of updates on its website, with the latest, at around 6.45pm blaming the problem in SY5 on a 'booster failure'.
The company said it expected to fix the problem in the "next few hours".
Duncan Spilsbury, who lives with his elderly mother at Shepherd's Lane, Bicton Heath, said it had been extremely frustrating.
The 49-year-old, who has been volunteering at Shrewsbury's vaccination centre, said: "It is one of the hottest days of the year today and they have not been round with any bottled water. The local Co-op has sold out.
"All day long it has changed from one thing to another. We were told this morning that the problem had been fixed overnight and it had not. We were told it was a pressure issue, then at 4.30pm we were told they needed to change one of the pumps."
He added: "We are under a Met Office warning for extreme heat. They do not make those things up for the sake of it."
A number of people in the Bicton area had posted on social media about the issues.
A spokesman for Severn Trent said: "We were unaware that anyone had been off supply in those areas since 8pm last night, we’ve recently received a call and discovered that eight properties had lost supply during that time.
"We are really sorry and absolutely mortified not to have spotted that earlier.
"We have bottled water on its way to those customers and we are working hard to get everyone back on as soon as possible.
"We are also making sure that properties around that area also have bottled water in case of any wider impact.
"Once again, we are really sorry to those customers that have lost supply, we know how frustrating it must be to be without water during this warm weather."