A fault at a Southern Water supply works has left tens of thousands of people without water and forced schools to close.
Southern Water said the problem had been caused by a "technical issue" at its Testwood Water Supply Works which meant low pressure or a loss of water supply.
Residents in Southampton, Eastleigh, Romsey and the New Forest have been left without water in their homes.
Southern Water said that the problem is affecting ten postcodes: SO15, S016, SO40, SO42, SO43, SO45, SO50, SO51, SO52 and SO53.
Ten schools have been forced to send pupils home, Hampshire County Council said.
The schools closed include: North Baddesley Infant School and Halterworth in the Test Valley, The New Forest Academy, Cadland Primary School and Wildground in the New Forest and Mountbatten School in Romsey.
Southern Water apologised to impacted customers and said it is working hard to restore water supplies by Thursday, but warned the issue might continue until the weekend.
It comes as the firm reported long queues at water bottle stations which have seen set up at the People at the Places Leisure Centre in Eastleigh and Sainsbury’s superstore in Southampton.
Southern Water said it is continuing to deliver water supplies to customers registered on its priority list and estimates around 58,000 homes have been affected by the issue.
It urged customers to avoid travelling to “other potential bottled water station locations until we confirm they are open”.
Southern Water said it has supplied dedicated tankers to Southampton General Hospital and Princess Anne Hospital, which are also affected by the issue.
“The fix at Testwood supply works is ongoing and we hope to complete the initial phase by tomorrow morning,” the firm said.
“We then need to re-charge our water network and restore supply to homes that were affected. If these works proceed to our current plan, customers should start to see supplies restored during tomorrow, but some areas may take longer.
“We are working towards all customers being back in supply by the weekend.”
A Defra spokesperson said: “We are aware of the water supply issues in Southampton and Marchwood.
"We are in close contact with Southern Water to ensure that the company is taking urgent steps to support residents and resolve the issue as soon as possible.
“The government has just announced reforms to double the compensation water companies provide to customers for supply issues like these and from next year, further investment into water infrastructure will provide a much-needed upgrade to services."
