The number of households on Boil Water Notices around the country is now down to 6,000.
Irish Water said that it has reduced the number from a peak of 23,000 customers who could not drink their supply straight from the tap at the end of last year.
The controversial state utility's announcement comes as over 200,000 homes in Dublin were told their water now has a lowered risk of cryptosporidium this morning.
The Environmental Protection Agency has signed off on the supply from the Stillorgan Reservoir in South Co Dublin after it underwent upgrades.
Irish Water spokesman Mark McAuley said that the latest improvements are to some of the country's oldest water facilities.
"With the introduction of a UV treatment unit, we now have removed the risk of cryptosporidium contamination in the water supply for the first time," he said.
"Which means that [for] 220,000 customers in the area, there's no risk of contamination."
David Flynn, programme manager of the EPA’s Office of Environmental Enforcement said: "The EPA Remedial Action List identifies 112 supplies - serving 770,000 consumers - that are in need of improvement to ensure the safety and security of these supplies.
"Thirty supplies on the Remedial Action List are in Co Kerry alone.
"Overall, the pace of investment in water treatment must continue to increase so that we eliminate the risk of cryptosporidium and the risk of long-term Boil Water Notices.”