Irish Water says it is making progress at dealing with at-risk water supplies.

It is reported the Environmental Protection Agency (EPA) is threatening to prosecute the utility when it fails to reach targets to fix supplies.

The Daily Mail reports that up to one million people could be exposed to contaminated water supplies, as Irish Water has failed to hit targets on essential repairs.

Jerry Grant from Irish Water says they have made significant progress on tackling Ecoli in supplies, but tackling cryptosporidium is proving more difficult.

Cryptosporidium is a parasite that causes the diarrheal disease, cryptosporidiosis. Both the parasite and the disease are commonly known as 'crypto'.

"It's a third of out population, of our supply system" he told the Pat Kenny Show here on Newstalk.

"It's important I suppose to put this in context - the biggest issue would be Ecoli breakthrough and that is largely dealt with, and we have a very high confidence level around that".

"The cryptosporidium risk is still an important risk - we still have nearly 10,000 people at risk of cryptosporidium".

But Mr Grant says they welcome the EPA's intervention.