Councillors criticised the reaction time of the firm to the "significant public health risk" affecting 31,000 households, describing it as disappointing and gravely concerning.

Read more: What we know so far about Northumbrian Water's problem in Darlington

A member of the council cabinet spoke of expletive-filled phone calls and an ultimatum to Northumbrian Water as the situation unfolded on Tuesday.

The fault at Broken Scar Treatment Works was raised at a meeting of Darlington Borough Council.

People in Darlington were warned to boil their water as a temporary precaution following the fault in the early hours of Tuesday.

The fault, affecting thousands of people living in some DL1, DL2 and DL3 postcodes, was said to be fixed but some water left the site without the correct level of disinfection.

Councillor Matthew Snedker raised the topic at the full council meeting on Tuesday night, saying: "There are many questions being asked of me.

"The broad brush is how long it took for the boiling water notice to come out from Northumbrian Water.

"We're aware that... contamination started yesterday evening. The notice to dispose of food that had been prepared yesterday evening is quite clear.

"The schools are very very concerned that food prepared on site and served throughout the day would have been with contaminated water.

"There would be businesses in the town who would have prepped food.

"For such a long delay before this notice came out, there's a lot of concern about the public health impact of this."

Cllr Kevin Nicholson, cabinet member for health and housing, read a statement saying: "We have a situation in Darlington which is compromising our drinking water.

"Northumbrian Water alerted the UK Health Security Agency of a failure that occurred at Broken Scar Treatment Works in Darlington which resulted in drinking water being contaminated with untreated water which does present a significant public health risk to residents of Darlington.

"This affects around 31,000 households, mainly in the central areas of the borough.

"A water boil notice has been issued. A water notice is going to be implemented immediately by Northumbrian Water to all affected households in the area, including by social media, radio and leaflets.

"This means that indiviuals should not drink water directly from the tap while the notice is in place. They should either drink bottled water... or heat water then cool it for drinking.

"The notice is likely to be in place for two to three days and will only be lifted once water sampling shows that water quality has returned to acceptable levels.

"Sites such as care homes have already been identified by Northumbrian Water and have been contacted to provide bottled water directly to them.

"Darlington Memorial Hospital has also been contacted directly, however their main drinking supply is via a separate borehole and we are taking appropriate action to minimise the impact on the hospital, patients and staff."

He said more incident response meetings were to be held in the evening and early hours.

Read more: Warning issued to residents after fault at water treatment works in Darlington

After the formal statement, he went on to say: "It is public knowledge that Northumbrian Water knew about the incident a little bit longer that had been advertised, which it's no secret will infuriate our health colleagues.

"Because ultimately once we know about a potential risk to public health it's best that we should act on that in order to protect those people with immuno-suppression diseases.

"So it does present me with a lot of concerns.

"As soon as the council were made aware, ie. me through our strategic command process, we put into place an immediate response to drafting members' communications.

"That all happened within 90 minutes. I couldn't have done it any quicker because I needed to get to the town hall to meet people face-to-face and to have those conversations with officers.

"We were in a position to work with Northumbrian Water because we did express concerns that they weren't moving quick enough. I personally expressed those to a number of colleagues.

"We did say to Northumbrian Water if they didn't go with the message at 4pm we would go with it ourselves because we felt that the risk was so high. In the end they did do that.

"We were doing everything we could in the background to try and encourage that but we do have to work in partnership.

"We will be working with the UK Health Security Agency to make sure that those vulnerable communities are supported.

"But there will be an investigation and the Member of Parliament Peter Gibson has raised this with the water minister this afternoon.

"And she's assured him that she's going to look into this and investigate how it's gone wrong."

Cllr Stephen Harker asked at what point Northumbrian Water understood there to be a problem, saying the statement was "vague" about the time of the incident.

He said: "I hence have a suspicion that they've known about it perhaps far longer than they're letting on.

"My concern therefore is... how long it took them to start telling people.

"The manner and the time in which they've chosen to act, I am gravely concerned about.

"And I'm pleased to hear that words have been said with them, but I do feel that it has been perhaps shambolic in terms of the speed with which they've chosen to act.

"I would suggest that they probably haven't been as quick and as responsive as perhaps they should have been.

"I appreciate hindsight's a wonderful thing, but... the sense I get... (is) that they have known about this for quite some considerable length of time."

Cllr Nicholson replied: "We acted swiftly and we informed Northumbrian Water of the serious public health concerns that both I and the public health director shared.

"It has been expressed to them, firmly, and not always in a way which others would have preferred.

"If you would have heard my phone calls this afternoon... you probably wouldn't be very happy with them. There was lots of expletives.

"But we moved as quick as we could've done.

"And I am equally disappointed with the slow pace at which Northumbrian Water operated and acted.

"It happened in the early hours of this morning so there was a significant time."

But he stressed there was a process with the UK Health Security Agency and unknown impact timeframes.

Cllr Bryony Holroyd expressed concern about the "slow" methods used to get information out like leaflet drops, and suggested using Northumbrian Water's text message service and phone calls through the priority services register.

She said: "It's all very well us trying to share information on social media but I suspect that the majority of our residents aren't on the particular social media channel that we may try to get the information out on."

Northumbrian Water has been contacted for a comment.

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