NI Water has asked โปรโมชั่น slotxo the public to "use water responsibly" as there is a "possibility" that a hosepipe ban may be introduced.
It said it had pumped 730 million litres of water into the system over the last few days.
That has increased from the normal distribution input of 580 million litres per day.
The company said potential hosepipe bans would be localised and would only affect domestic customers.
Tankers are moving water into areas that are facing the biggest supply shortage.
Cookstown, Magherafelt, Newcastle and Banbridge are among the areas at most risk of water restrictions, NI Water has said.
Des Nevin, director of customer and operations, told BBC Radio Ulster's Evening Extra programme, that areas at risk of a hosepipe ban included:
Lough Fea Water Treatment Works in County Tyrone, which feeds into Cookstown, Magherafelt, Draperstown and Desertmartin
Castor Bay Water Treatment Works in County Armagh, which feeds into Banbridge, Newry and Dungannon
Areas of Newcastle and Kilkeel in County Down
The Department for Infrastructure said it was in regular contact with NI Water "during this period of extreme heat" and "called on the public to use water wisely".
An amber warning for heat has been issued for Northern Ireland from Wednesday until the end of Friday.
NI Water said people needed to reduce their water use or risk running dry.