Thousands of people have been left without water on Sunday due to an issue at a Thames Water treatment works.
Thames Water apologised to residents in Godalming, Surrey, and said it was investigating.
Jeremy Hunt, the MP for the area, said a major incident had been declared. He posted on X, formerly known as Twitter, that he was very concerned and had spoken to the CEO of Thames Water.
It follows issues caused by Storm Ciaran at Shalford water treatment works, Thames Water said.
Mr Hunt said he was told by the CEO at 2.50pm that 13,500 customers did not have water and a further 6,500 were expected to lose supply shortly.
The site controls had been reset and were being tested, he added.
Bottled water stations have been set up at the Crown Court car park in Godalming and Artington park and ride in Guildford.
Thames Water said it was also delivering bottled water to vulnerable customers.
However, one person whose elderly father was affected by the water supply problem said he had been unable to arrange a bottled water delivery.
Richard Davies told Sky News he had contacted Thames Water to arrange delivery to his 84-year-old father, who lives in Guildford and is immobile after a hospital stay, to be told there was no alternative supply and the adviser had not been updated about any bottled water.
"It's worrying how many people without transport or relatives could be currently without any help from Thames Water," Mr Davies said.
"To leave an 84-year-old man without water whilst publicly saying they are looking after their vulnerable customers is nothing short of disgusting."
After being contacted by Sky News, Thames Water said they had contacted Mr Davies and organised a delivery of bottled water for his father.
A spokesperson said: "We are sorry to hear that one of our customers had trouble securing a bottled water delivery. Our dedicated customer service team have since been in touch to arrange a delivery and will add him to our database to ensure this does not occur again."
In a later update Mr Hunt said he had heard from Surrey Gold Command and the CEO of Thames Water that the company was hoping to bring the Shalford treatment works "back online within the next hour having identified the cause now".
"They have significantly reduced water turbidity and are hopeful that the alarms will not trip once it has gone through the gravity filters. They won't know for sure until early evening but looking more promising," he tweeted.
"However, if successful the disruption will continue overnight and during tomorrow. Bottled water getting to vulnerable communities and water tankers to local hospitals."
In an update at 7pm, he said he had heard Thames Water "now have water going into supply and will be ramping up production rates over the next three hours".
"Still some risk but remains promising that a solution may be in sight," Mr Hunt added.
Surrey County Council confirmed a major incident had been declared in the area, telling Sky News it was "due to the number of properties affected" and also due to the incident occurring on a Sunday, when fewer staff are around.
In a separate statement the leader of the council, Tim Oliver, said: "Surrey County Council is continuing to work with partners across the Local Resilience Forum (LRF), following notification from Thames Water of a water shortage in the Guildford/Waverley areas.
"This has been declared a major incident by the LRF. All partners will continue to work closely with Thames Water, who are the lead agency in this incident, to inform and support residents in these areas, particularly those most vulnerable."
Thames Water said its engineers were on site and tankers were being used to pump water into its supply network.
A Thames Water spokesperson said: "We're sorry to people across Guildford, Godalming and surrounding areas who have no water or lower pressure than normal.
"Our Shalford water treatment works has been affected following issues caused by Storm Ciaran. We have engineers on site who are working around the clock to get things back to normal.
"We also have extra support measures in place for our most vulnerable customers and have been delivering bottled water to those on our priority services register since Thursday and have continued to do so across the weekend.