An RTÉ investigation has discovered the source of the contamination of drinking water in Cavan and Monaghan.
In April, the drinking water of 10,000 people was poisoned with Phenol, a toxic and caustic chemical.
The RTÉ Radio Investigative Unit has established that a waste product from the copper mining industry was used in place of a water treatment chemical, and that is what is responsible for the phenol contamination.
Subscribers to five group water schemes in Cavan and Monaghan started complaining of blisters and sores in their mouths and a range of stomach complaints in April.
The Radio Investigative Unit has now established that the source of the Phenol contamination was a tainted water treatment product, aluminium chloride.
It had been supplied by the Cork based environmental solutions company Enva.
Enva sold an unwanted waste product generated by the copper ore mining industry as being suitable for the treatment of drinking water.
While it says that it specifically told the end user that the product was not suitable for drinking water, the technical data supplied with the chemical suggests otherwise.
This product cost a fraction of the properly synthesized chemical and contained traces of phenol.
The end user of this chemical, the French water treatment services giant Veolia, has admitted to RTÉ that it did not observe European guidelines and standards when purchasing the aluminium chloride.
The product it had bought from Enva through an intermediary was about two-thirds the price of other market competitors.
Enva has told RTÉ that it is co-operating fully with a multi agency investigation into the incident and believes it would be inappropriate to comment any further while this investigation is ongoing.
The company adds that they are fully confident that the investigation will show that Enva has acted appropriately at all times.
Water supply has been returned to the subscribers of four of the affected schemes in Cavan. The precautionary ban in Glaslough, Co Monaghan remains in place.
