Consumers are being asked to preserve depleted water stocks or face potential hosepipe bans as large parts of the UK continued a spell of several weeks without rainfall.
Britain saw its 16th consecutive day where temperatures above 28C were recorded on Monday, the longest such spell in five years.
The heatwave has also brought an extended period of dry weather, leading several utilities companies to issue warnings to customers over usage.
United Utilities, which serves northwest England, said it was not looking to introduce a hosepipe ban imminently thanks to a drop in water usage on Monday.
However, it says it could still be forced to take the measure if high demand for water did not continue to ease this week.
The company had moved water from north Wales this week to replenish depleted stocks across the region during the drought.
In Northern Ireland, a hosepipe ban has been in effect since June 29, with an extra 175 million litres of water being pumped into the network in a bid to keep up with demand.
“We have maximised our water production and need customers’ help to reduce demand,” said Northern Ireland Water chief executive Sara Venning.
“We are asking customers to take heed of the hose pipe ban and stop non-essential water use – using hoses and sprinklers is causing demand to exceed the capacity to supply.”
Weather is expected to stay dry on Wednesday across most of the UK, although temperatures are likely to drop towards the low 20s in many areas, according to the Met Office.
As Thursday approaches, forecasters warn there is the potential for rain and even thunderstorms to hit almost anywhere, with northern areas particularly at risk.
Friday, however, will see a return to warmer conditions, with temperatures expected to rise day-on-day over the weekend.
In the southeast, the mercury could once again break through the 30C mark on Saturday and Sunday.
“Monday was our sixteenth consecutive day where we have seen temperatures above the 28C mark, we are in the midst of a heatwave,” said Met Office meteorologist Dean Hall.
“Obviously it has been very dry, gardeners will be aware of that, a lot of lawns will be looking pretty scorched and brown at the moment and a bit of rain is probably going to be pretty welcome by the end of the week.
“However, it still looks as if parts of the south east will be getting away with a lot of fine and dry weather, they may escape the more changeable conditions in northern and western areas.”