Wessex Water has been hit with a £280,000 fine after it provided customers with undrinkable water for three weeks.
The company has also agreed to pay out more than £21,000 to its affected customers.
The fine was handed down by Swindon Magistrates following prosecution by the Drinking Water Inspectorate.
Wessex pleaded guilty to the offence under section 70 of the Water Industry Act 1991 for the supply of water unfit for human consumption.
The offence relates to a three-week period from the end of March 2021 when consumers in the Amesbury area of Wiltshire complained of an unacceptable taste to their tap water which made the water undrinkable.
The cause for the objectionable taste was due to Wessex failing to undertake the required checks on the carbon filter which, if completed, would have identified the presence of iodinated organic compounds leaving the treatment works.
The Inspectorate criticised Wessex for failing to follow its own internal testing procedures which would have identified the presence of the taste causing compounds. There were also issues reported with the communication given to consumers and provision of alternative water supplies.
Marcus Rink, chief inspector of the DWI, said: “Consumers experienced water with an unpleasant taste which would not have happened had the required checks been carried out on the carbon filter before it was brought into use.
“This prosecution acts as a reminder to companies that a water quality first approach must be taken when providing a service to the public. I am content that the court has recognised the seriousness of this event.”
The inspectorate added that the company has experience of similar events within its operating region from sites which use carbon treatment, yet the lessons learnt from these previous events did not prevent this issue from happening.
Since the event the company has taken corrective measures including strengthening its own internal procedures which cover returning carbon filters to supply.
A Wessex Water spokesperson added: “We’re sorry to those customers who noticed a difference in the taste of their water when we supplied water not of the usual high standard. We acted quickly to resolve the problem, notified customers promptly and apologised.
“Until now, we were the only UK water and sewerage company never to be prosecuted for a water supply incident. We have since put steps in place to prevent this from happening again.”