Water misery has returned for about 24,000 households in Kent and East Sussex with a water firm saying they do not expect supplies to be restored to all affected customers until midday on Thursday.

South East Water (SEW) announced on Wednesday – after five days of problems – the supply issues had returned to all affected properties due to a “water quality issue” and warned the public to boil water before drinking.

Schools have been closed, and residents have had to rely on neighbours across the affected area.

The water station at RCP Parking’s site on Major York’s Road near The Pantiles will not be open on Thursday due to an event taking place at the Spa Valley Railway, SEW said.

Bottled water stations at Knights Way and Tunbridge Wells Sports Centre, and a grab bag station at the B&M store, will reopen on Thursday morning.

Speaking at Prime Minister’s Questions in Parliament Sir Keir Starmer described the situation as “shocking”.

Tunbridge Wells Borough Council confirmed on Wednesday it had declared a “major incident”.

The prime minister added he was aware that South East Water had consistently failed to meet its promises of restoring a safe supply of water in the past few days.

Responding to a question from Liberal Democrat leader Sir Ed Davey, who asked him to convene an emergency meeting on the matter, Starmer said: “There’s really serious consequences and we are bearing down on that as he would expect because it’s such a serious issue.”

Businesses in Tunbridge Wells have said they are set to lose earnings as a result of the water problems.

Birkan Koca, who runs Eggs Eleven cafe in the Pantiles, said the response from SEW had been “shambolic”.

“If the water isn’t back on by the weekend we could be looking at £15,000 worth of losses,” he said.

Grace Power, who lives in Tunbridge Wells, said she had gone to work in London on Wednesday as she was unable to work in the Kent town.

She has two children under the age of five, is pregnant and is worried about the water quality.

“We had our water supply return on Tuesday, and South East Water said it was safe to drink,” she said.

“We are now being told it must be boiled before consuming.”

Eden Hedges, from St Kilda Cafe, said there had been a “lack of specific information” which “left him in the dark”.

He said the new boil notice had made him worried about whether the filtration units in the coffee machines would be able to make coffee.

“If I knew why I have to boil my water, I would then be able to make a judgement on whether the machines could make it safe,” he said.

SEW said on Wednesday afternoon it did not expect supplies to be restored to all affected customers until midday on Thursday.

It said this was because the pipeline network in Tunbridge Wells was being “gradually refilled” to avoid any more issues, including burst pipes.

Emma Hardy, government water minister, told BBC South East there would be a “full investigation”.

The company had said supplies were back for 12,000 customers on Tuesday.

Its head of water quality, Dr Neil Hudson, said after recharging their network in Tunbridge Wells they saw a “recurrence of the water quality issues” which caused the initial shutdown of the water treatment works in Pembury.

“Because of this, we are currently unable to produce drinking water from the Pembury treatment works that meets the strict regulatory standards required for consumption,” he said.

He urged residents to use water only for flushing toilets or showering, and said water could not be “used for drinking and cooking without boiling first”.

The problem, which began on Saturday, has seen customers in Tunbridge Wells, Pembury, Frant and Eridge experience a loss of water or low pressure.

The company blamed a “bad chemical batch” as the source of the problem.

Four bottled water stations will remain open until 22:00 GMT on Wednesday at Tunbridge Wells Sports Centre, RCP Parking, Odeon Cinema Knights Way and The Amelia Scott.