The fallout from parasite-contaminated water in part of Devon cost South West Water £16m, the utility has revealed.
It had to implement a boil water notice when people in the Brixham area became sick after diarrhoea-causing cryptosporidium was found in a reservoir in May.
The notice remained in place for eight weeks with roughly 17,000 households told to boil their drinking water.
South West Water said on Thursday morning it had to clean and flush its water network 27 times and replace sections of the 30-kilometre grid to restore supply to customers.
Staff worked “24 hours a day”, the company said, and installed additional water treatment measures on the network such as ultra-violet treatment plants.
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Further costs came from running bottled water sites for customers. The drinking water pollution is believed to have been caused by cattle manure getting into a damaged air valve in a farmer’s field.
But the cost could have been higher if government compensation proposals had been enacted at the time.
Under reforms announced by Environment Secretary Steve Reed, water companies will have to pay households when boil water notices are issued.
Mr Reed is seeking to more than double compensation sums and will consult on upping remuneration.
In May, parent company Pennon revealed it was paying out about £3.5m in compensation to customers affected by the parasite outbreak.
In its latest financial report, it announced an 8.6% increase in underlying operating profits to £166.3m.
While water in the Brixham area is now drinkable again, keeping water clean has been challenging for the firm due to “higher than normal rainfall” and groundwater levels, Pennon said in a trading update.
That has impacted the number of pollution incidents and the “performance of a small number of treatment works”, it added.