United Utilities (UU) said on Thursday that water samples taken in the Lancaster and Morecambe areas had revealed no health risk.

It said a lightning strike may have been the cause of a power surge at the Lancaster treatment works which disrupted water treatment on Monday.

Customers had been advised since then to boil their water before drinking it.

But the company said that had just been a precautionary measure and no samples had revealed anything harmful in the supplies since then.

UU's customer service director Gary Dixon said: "May I thank customers for their patience and co-operation and apologise for any inconvenience caused.

Lightning strikes

"I am sorry that customers were asked to take this action but it was a necessary precaution until we could confirm through additional sampling that supplies had not been affected.

"Water supplies were monitored throughout and the advice to boil water has been withdrawn as soon as possible."

Engineers will now look at ways of minimising the impact of lightning strikes on the water supply in the future.