Water companies are asking customers to conserve supplies as Britain continues to bask in a heatwave.
Northern Ireland Water will introduce a hosepipe ban from this weekend to stop any interruptions to supplies.
The hot weather is expected to last with the sun set to shine into the weekend across most of the UK, as water companies said usage had been "significantly more" than normal.
NI Water chief executive Sara Venning said the company was appealing to customers to stop non-essential use, as hoses and sprinklers were causing strain on supplies.
She said: "In recent days our treatment works have been operating at near maximum levels with over 700 million litres of water being put into the network, which is some 25% more than is normal for this time of the year.
"Despite these steps, demand continues to outstrip supply.
"It would be our intention to introduce a formal hose pipe ban in an effort to protect the public against the increased threat of supply interruptions."
Huge spikes in demand for water at mornings and evening peak times mean utility companies 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.
Severn Trent is asking people to be "neighbourly" and use water carefully, while United Utilities and Anglian Water are among other firms who have issued advice on cutting down on water use.
Doug Clarke of Severn Trent said: "Demand for water is massively up thanks to several weeks of extremely hot weather.
"While we have lots of water available and our reservoir levels are healthy and we're putting millions of extra litres of water into the system, people are using water as fast as we can treat and pump it into supply.
"This is particularly the case during peak demand in the morning and evenings when we want to ask customers to restrict their supply so we can avoid areas of low pressure."