United Utilities accepts it is facing a colossal compensation bill for the first cryptosporidium contamination of drinking water in the North West UK this century.

But the company has reassured consumers the payouts – estimated already at £15m and mounting – will not be offset by a rise in water bills.

“Bills will not increase to cover the cost of compensation,” insisted a spokesman.

“This cost will be borne by the company.”

With more than 300,000 households and businesses hit by the scare, now into its third week, United Utilities has declined to put a figure on how much the crypto invasion will amount to.

But in a recent case in Bolton, where consumers had to boil their drinking water for five days after supply problems, the company paid out £15 per house to cover the cost.

With the inconvenience to customers in Preston, South Ribble, Chorley, the Fylde Coast and villages like Samlesbury, Mellor and Mellor Brook at least three times that already, claims could amount to at least £45 a household, or £13.5m in total.

With businesses set to lodge much higher demands for compensation after providing bottled water to all employees during the scare – BAE Systems is thought to have spent more than £100,000 already on keeping its 10,000-strong workforce in Lancashire hydrated – the bill is estimated to be rising by £1m a day.