With the heat wave set to continue for the foreseeable future, the company has not ruled out introducing a hosepipe ban.
It is warning a significant number of people may lose their water supply if the high demand continues.
A NI Water spokesperson said: “With extreme high temperatures over the last few days, customer demand has significantly increased and is outstripping supply.
“It is important our customers reduce their demand as soon as possible. If everyone simply uses the water they need for the essentials, there will be enough for everyone.”
Both towns are understood to be under the greatest pressure as they struggle with increased water usage
.Des Nevin, director of customer operations, said: “If demand continues at this level it will lead to failures in our network 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.
“On Monday 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.”
Some of the easiest tips to save water that can make a massive difference include: avoid watering lawns; buy water efficient plants; buy pots made from plastic, terracotta or wood.
Turn off the tap while brushing your teeth; make full use of your washing machine; take shorter showers; take a shower instead of a bath, and avoid washing cars or vans, use a bucket and sponge.
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