Welsh Water has admitted it has to work to restore consumer confidence after the stomach bug outbreak which hit Anglesey and Gwynedd.
The boil water order was brought into force in late November
Welsh Water head Nigel Annett said £1m of extra ultra-violet treatment had been installed to prevent a repeat.
But he said the company knew the problem had caused "enormous upset, inconvenience and cost" to customers.
Two months after 70,000 people in the area were told to boil their drinking water, the order will be lifted soon.
Welsh Water is expected to announce imminently that people can stop boiling their water.
The restriction was first imposed at the end of November after the first cases of the water-borne bug cryptosporidium emerged.
The order had been due to be lifted early in January, but that was delayed.
It has caused problems in large parts of north Wales for households and businesses.
Mark Bartlett of the Gwynedd Hotel in Llanberis said: "The last few months have been extremely difficult and it's small things that people don't even think about."
New treatment equipment has been installed at the reservoir
He said cleaning out beer lines took days, rather than hours.
"Imagine how much water you have to pre-boil to clear nine, ten lines of beer. It takes forever," said Mr Bartlett.
"Spirits and shorts have dropped by 90% in sales because people wanted ice in their drinks. Financially, it's hard to put a figure on it but it's probably several thousand pounds."
The source of the bug was thought to be the Llyn Cwellyn reservoir, but that has not been confirmed. To date, about 230 people have fallen ill with the bug.
Mr Annett, Welsh Water's managing director, said its extra treatment at the reservoir was the first of its kind in Wales and England, and would guarantee that it water was free of "even very background levels of the spore which may have been implicated in this outbreak of illness".
He said: "Cwellyn is one of our very best water treatment works across Wales and it has been operating perfectly normally throughout this entire period.
"All we have seen is very, very background levels of this cryptosporidium spore in the water supply and that normally is not associated with illness.
"The water supply has been implicated as a possible source of this problem but has not been confirmed as such. We don't know, the health experts don't know. We've been looking at every possible cause."
People in the affected area will receive £25 compensation which he said was "almost exactly equivalent to the cost for an average household in Wales for two months' water supply".
Mr Annett said: "We fully appreciate that we have caused enormous upset, with the health people.
"It was a precautionary move by the health people to issue this boil notice: we went along with that.
"But we do recognise the inconvenience and cost we have caused to 70,000 people living in Anglesey and Gwynedd and we have a job of work on our hands to restore public confidence over the coming weeks and months.
"But I would say that additional treatment we've put in at a cost of over £1m will at least take water supply off the list of suspects as a cause of this problem in the months and years ahead."