The public has been urged to urgently reduce water usage to avoid shortages.
NI Water has warned that, due to recent hot weather and people holidaying at home, the current demand for water is outstripping supply.
Director of customer operations Des Nevin said if the current demand continues, it will lead to failures in the system and some customers will lose supply or suffer low pressure.
“A number of customers over the past few days are already experiencing this, especially those on high ground,” he said.
“Yesterday we put 695 million litres of water into our distribution system, this is over 120 million litres more than normal.
“We are asking our customers to help us, especially over the next few days when temperatures continue to be high. We know from the increase in our night usage some customers are leaving sprinklers and hoses on overnight, please stop.
“A hose uses more water in one hour than the average family uses in a whole day. A pressure washer can also be a massive drain, so please think about whether the task is really essential at the moment.
“While it is tempting, please avoid using swimming or paddling pools this weekend. Filling a 12ft swimming pool uses the same amount of water 500 people use for daily handwashing.
“We want everyone to enjoy their home and garden, we just need people to think about how they use their water and if what they are doing is essential.”