Customer complaints about Irish Water fell by nearly 20% last year, according to the Commission for Energy Regulation.
The commission dealt with 650 issues raised by Irish Water customers in 2015.
But the commission thinks the higher volume of issues in 2014 may have been due to the introduction of water charges that year.
The commission dealt with almost 4,000 complaints in 2015 - from gas, water and electricity customers.
The largest number of complaints were about Bord Gais Energy.
The company has a 23% share of the gas and electricity market, but accounted for over 40% of complaints.
Three quarters of complaints about energy suppliers related to problems with bills.