Water supplies in Wirral have returned to normal after a faulty valve was repaired, ending more than a week's worth of disruption for residents.
United Utilities has confirmed that people will be compensated after two separate problems led to thousands being left without water last weekend.
The company said the problems had now been resolved after valves had been repaired.
The firm thanked residents for their patience.
Scott Beard, United Utilities' regional water network manager, said a full investigation would now be carried out.
He said: "Our engineers have worked around the clock to rectify a succession of problems that have arisen since we isolated one of the major supply feeds into the Wirral to repair a leak.
"We have done our best to keep people updated."
He added: "It has been very difficult given the fast changing situation and the scale of the area affected but I understand the frustration this caused and we need to see how we can do better in future."
The problems began on Thursday 20 May when emergency repair work on a burst water main led to 15,000 customers in Moreton, Leasowe and Wallasey being cut off.
About 4,500 homes in the Wallasey area then suffered with low pressure or no water at all because of a faulty valve.
Water supplies were restored to most customers by pumping water directly into the system using tankers
But fluctuations in pressure meant that some customers in the Wallasey area lost supply temporarily and others on higher ground had intermittent supply.
The water mains network and all supplies were restored to normal at 0600 BST on Sunday, United Utilities said, after two days of repairs.
Mr Beard added: "To have two major problems like this at the same time is extremely unusual.
"We will be carrying out a full investigation to assess what contingencies we could have put in place to help restore water supplies for our customers more quickly."