Work is under way to repair a faulty water mains valve, which has disrupted supplies to homes in Wirral.
Repairs to the 36in (91cm) valve began overnight but United Utilities said it will take two days before the network returns to normal.
Tankers are pumping extra water into the mains and supplies are being re-routed along different pipes to reach residents.
United Utilities said it was also attending two minor bursts nearby.
About 20 houses on Noctorum Avenue and Wirral Way are thought to be affected by the latest bursts.
United Utilities said that teams were already on site and that bottled water was being offered to affected residents.
It is thought that a broken spindle caused the fault to the mains valve in a pipe under a field in Upton.
United Utilities said engineers had emptied 1.4 million litres of water from the pipe into Fender Brook, near Prenton.
Scott Beard, regional water network manager, said: "We have done a lot of planning for this delicate operation and I'm pleased to say that it is going to schedule.
"It is a huge and complex operation and we are monitoring water supplies very closely as we continue the complex process of repairing the valve and re-commssioning the pipe."
United Utilities confirmed that people would be compensated for the disruption.