Yorkshire Water could take criminal action over a contamination crisis which affected more than 3,600 people in Thorne and Moorends.
The company says it has identified the source of the E.coli bacteria and is considering whether to launch proceedings under the Water Supply (Water Fittings) Act.
Neil Dewis, head of service delivery, said a company had ‘modified’ its pipework but failed to call in Yorkshire Water to inspect it - a legal requirement.
More than 100 people worked to combat the contamination after concerns over discolouration were raised by the Real Yorkshire Pudding Company on Coulman Industrial Estate on July 28. The firm is not the source, Mr Dewis said.
Samples were found to contain E.coli - potentially affecting 3,600 premises - triggering emergency procedures.
A ‘do not drink’ order was downgraded to a ‘boil order’ at 4pm on Saturday. Water was finally declared safe to drink on Thursday.
Mr Dewis said the firm’s response had been ‘excellent’ and also praised the local community, the council and the Red Cross.
He added: “When E.coli was discovered we went back to a number of units on the estate and identified concerns in one. We immediately isolated the unit from the network.
“We will be investigating and could take action under the Water Act.”
An incident management team swung into action to notify customers at 3,648 properties by text, social media, on its website and with visits to vulnerable customers with the help of Doncaster Council, he added.
Some 250,000 litres of bottled water were provided at two sites while 35 staff delivered bottles to homes.
Goodwill payments of £30 will be sent to customers in the coming days.
Mr Dewis said there were lessons to be learned, confirming up to 100 people from an initial list of postcodes had been contacted by mistake.
“We sincerely apologise for the inconvenience to people.
“There are always lessons to learn around how to communicate.”