The High Court has ruled the practice of slopping out endured by a prisoner in a shared cell at Mountjoy Prison was in breach of his constitutional right to privacy.
However, the court also ruled the prisoner in question was not entitled to compensation.
In what could be seen as a test case for hundreds of others, the court ruled the practice did not amount to inhuman and degrading treatment.
The court also refused to award any compensation to ex-prisoner Gary Simpson as Mr Justice Michael White found he was an untruthful witness who had exaggerated parts of his evidence.
The judgment could affect hundreds of similar cases taken by former prisoners over the practice of slopping out.
In his High Court Simpson claimed his human rights were violated and that he felt humiliated and degraded by the slopping out regime in place on a particular wing of Dublin's Mountjoy prison while he was a prisoner there for eight months in 2013.
He was serving a three-year sentence for robbery and had requested a transfer to D1 wing for his own safety.
While in that wing he said he was subject to a 23-hour lock-up. He had to share what was designated a single cell and had no toilet facilities or running water.
Prisoners had to use basins and other items as a toilet and empty them the following day. Prisoners on D1 wing also had to eat in their cells, the High Court was told.
Lawyers for Mr Simpson said he felt low self-esteem as a result of the slopping out regime and experienced feelings of anger, humiliation and a "sense of worthlessness".
The slopping out regime was condemned in 1993 by the European Committee on the Prevention of Torture and was also criticised in a range of reports, including by the State's Inspector of Prisons.
In 2010 the State began a programme of prison refurbishment with a goal of single cell occupancy and in-cell sanitation.
In his judgment this morning Judge White said a prisoner’s constitutional rights were restricted but not "totally set at nought".
He said in Irish constitutional law the practice of slopping out had not been found to be unconstitutional, nor had the lack of running water in a cell.
He said in the case of Simpson there was a "unique set of circumstances" and he was critical of the amount of space in the cell due to the "doubling up" of prisoners.
The judge said he had huge issues with the credibility of Simpson and had rejected portions of his evidence while accepting other parts.
He said there was a restricted regime regarding showers and it was "difficult, if not impossible" to get out to the toilet during the day.
However he said the court had taken a view that it was not appropriate to make a declaration that the treatment amounted to torture or inhuman or degrading treatment.
The judge said it was a "balancing exercise" and said he must have regard to the totality of treatment of prisoners.
He also noted there was a clear intent to refurbish Mountjoy and work was ongoing on the refurbishment at the time.
However, he said, within the shared cell the chamber pot used by prisoners was on the floor and there was no modesty screen provided.
Such a screen would have gone a long way towards giving better respect to a prisoner’s right to privacy, the judge said.
He also said in 2013 the prison was facing a very clear direction from the Inspector of Prisons that only in exceptional circumstances should prisoners be doubled up in cells where there was a 23-hour lock-up.
The direction in this regard "could not be clearer" the judge said.
Taking all matters into account, he said the privacy rights of Simpson had been breached.
However the court "could not contemplate" awarding damages because of his lack of credibility as a witness and his untruthful evidence.
Department says 98% of prisoners have in-cell sanitation
The Department of Justice has issued a statement saying it notes the judgment.
It said a Department official was present in court and the final written judgment will be carefully considered in due course when it is published.
It added that the Government has made significant progress in ending the "slopping out" in recent years and continues to prioritise this issue.
Over 98% of prisoners across the prison estate have access to in-cell sanitation and on completion of the upgrade projects at Limerick and Portlaoise prisons, "slopping out" will be completely eliminated across the prisons estate, the Department said.