The firm has enacted its contingency plans and increased water production capacity in order to meet the anticipated spike in water use as the warm weather continues.
Irish Water announced the ban will come into force from 8am, saying Ireland is trying to "manage with the summer".
People will not be allowed to use a hosepipe to water their garden or potted plants, wash their auto or boat, or fill a paddling pool, pond, or water fountain.
It's extending its hosepipe ban beyond the Greater Dublin area this week, as part of efforst to counteract falling reservoir levels during the heatwave. Both companies say supply is healthy, but they have stressed the importance of not wasting water.
'Irish Water thanks the public for their conservation efforts to date and we continue to encourage and support the public in their efforts to reduce usage.
The ban is being introduced by Irish Water who have warned of drought conditions due to the prolonged heatwave.
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The Irish Times indicated that Dublin water consumption levels have reached an all time high of 615 million litres a day, last week.
On average demand across all water resources nationally has increased by 15%, and given the environmental pressures on the aquifers and waterbodies, this can not be sustained for any period of time. Along with its plea, Irish Water has placed schemes to help fix leaking pipes on properties with the "first fix to be free" - they are hoping that these measures will help to prevent water wastage.
The group included Met Eireann, the Dept of Housing, the HSE, Gardai, Irish Water and other groups.
As well as reducing consumption, we are appealing to the public to report leaks on the public water network to 1850 278 278 and to fix private side leaks in both homes and in businesses. Based on modelling in previous dry years, and allowing for how dry the ground now is, we need to maximise conservation of raw water at this time to secure our needs over the coming months. Network leakage is approximately 37% of water supplied today in this region and Irish Water has commenced work on a major leakage reduction programme which replicates what has been done in Britain and Northern Ireland where levels of 20-25% have been achieved after decades of major investment.