Irish Water received nearly 1,800 complaints last year including 474 from people claiming they had got sick due to water quality issues.
There were also 479 who contacted the utility, which has recently rebranded as Uisce Éireann, to say that discoloured water was flowing out of their taps.
Another 28 complaints were logged from customers who said there was a funny odour from their drinking supply while 82 said their water tasted strange.
Nearly a third of the complaints, 557 in total, were about water outages where no supply was available at all while 15 people contacted the utility to complain about drinking water restriction notices.
There were also 57 gripes from people about boil water notices, where they had been informed that their tap water was not safe to drink.
Overall, 1,790 formal complaints were logged with Uisce Éireann with at least 200 recorded in each of August, September, and October, the three busiest months for complaints.