Irish Water has said it expects to reduce the number of water treatment plants requiring serious upgrading to below 100 this year.
It comes after the Environmental Protection Agency said significant investment is needed to address quality issues in water supply systems serving almost one million people.
The EPA has said 121 water supplies are at risk due to inadequate disinfection and water management systems.
Speaking on RTÉ’s Today with Sean O’Rourke, Head of Asset Management Jerry Grant said Irish Water will also make significant improvements to the operations of its plants.
Mr Grant said that, for water supply alone, Irish Water needs €2.3bn to invest between now and 2021, adding the majority of revenue has to come from customers
The EPA found a small proportion of Ireland’s drinking water supplies fail to meet the microbial and the chemical standards required for safe drinking water.
But the EPA said the good compliance rate masks the specific and serious problems occurring in some supplies around Ireland and the significant risk of future problems.