Almost one-third of the country's private water wells are contaminated by E.coli, a new report has found.
According to the Environmental Protection Agency (EPA), this means that up to 50,000 drinking wells in Ireland could be contaminated.
The Central Statistics Office states that there are approximately 170,000 private wells in the country.
The EPA has warned that it is riskier to use your own water source as opposed to using a main supply.
"What is not generally known is that there is a greater risk of illness associated with private well supplies," stated a spokesperson from the body.
The agency also said that immunity can be built up to the bacteria but for friends visiting your home and drinking from the well it is dangerous.
"You may have been using your well for years and have had no health problems as you may have built up immunity to the contamination.
"However, friends, family and children may become ill as a result of consuming your well water," said the spokesperson.
The EPA listed a number of things that private well-owners can do to ensure that their water is safe to drink.
It said to make sure that the lid or well-head is sealed properly and also to ensure that no surface water can get into it.
Other sources of contamination can include nearby septic tanks and chemicals or fuels stored in close proximity to the well. The environmental agency also recommended that a well is serviced once a year.
"Just because the water comes from underground does not mean it is OK," said the spokesperson.
And the "most common problem" associated with them is poor construction.
Separately last month, a row broke out in the Dail over water bills being sent to homes where the water was not fit for purpose.
Fianna Fail leader Micheal Martin said it was monstrous that families were to be charged for something that could make them sick.