VIDEO: Kettles 'popping' as they boil
Hundreds of people have taken to social media to complain that their kettles are "going off like popcorn" when they boil them.
Residents across West Cumbria say tap water is smelling odd and a scum has appeared on the surface of the water.
Some people are no longer using their tap water while others have had to buy new kettles.
United Utilities said it was absolutely safe and occurred due to the blending soft water from Ennerdale with harder water from boreholes in Egremont.
Cheryl Corlett, of Kells, said the weird development had put her off using her tap water.
She said: "I noticed a week ago the kettle popping when boiling but thought it might have been on its way out and I was just going to use it until it gave in.
"I only noticed the smell of the water on Saturday.
"I noticed, when making a cuppa, the water turns black in about two seconds as if the tea's been brewing for ages and what I would call bubbly scum in cups of tea as if the milk's curdling or something.
"When I wash dishes they still have a funny smell on them. It's weird. United Utilities said there's no issues but it's not normal so I'm not drinking anything using the tap water.
"It isn't normal even though they say it's safe but I'm not taking any chances until they confirm whatever it is."
She sent us a video of her kettle popping as it boiled.
On the Whitehaven News Facebook page, Cheryl Barwise said: "Here in Gosforth, we noticed it's been popping for the last few days. Ours is clear glass with a chrome bottom and it's gone brown really fast.
"It also has a scummy froth in tea cup, I also drink a lot of water and it tastes different."
Derek Edge said: "We use leaf tea and lately there has been an unusual scum around the side of the mugs.
"I thought it was an issue with Tesco brand tea but now realise it's probably the water."
A United Utilities spokesman said: "We are aware of reports of a popping noise from kettles when being boiled in parts of West Cumbria and we would like to apologise to customers if this has caused concern.
"Customers in the Copeland area may have noticed a slight change in their water supply in the last couple of weeks.
"This is due to us blending water from Ennerdale, which is soft, with harder water from boreholes in Egremont.
"Our regular water samples show that, despite the popping noises, the water supply meets all water quality standards.
"The popping noise can be explained by tiny bubbles forming and collapsing as the water boils and is due to the slightly harder water.
"Blending water from different sources is absolutely safe to do and we have been blending these water supplies for a while but have recently increased the proportion from the boreholes further than before.
"It's all part of the short term aim to balance the amount of water we take from Ennerdale to protect local wildlife, while continuing to meet the demands of the local community.
"Abstracting water from Ennerdale will completely stop in the long term once the new £300 million pipeline linking West Cumbria to Thirlmere Reservoir is complete."