This charming story is associated with Áed Uaridnard, who was one of the senior Northern Uí Neill chieftains. According to the source, he was passing through monastic land controlled by Saint Muru when he stopped to wash in the river flowing through the town. As he did so one of his men warned him not to do so.
‘Oh, rí. Do not put that water on your face.’
‘Why not?’ asked the rí
‘I’m ashamed to say,’ he said.
‘What shame is on you for telling the truth?’ asked the rí.
It’s this. The clerics latrine is over the water.’
‘Is that where the cleric, himself, goes to defecate?’ asked the rí.
‘It is. indeed,’ said the youth.
‘Then, not only will I put it on my face,’ said the rí. ‘I’ll also put it in my mouth, and I’ll drink it – drinking three gulps of it – for the water his shit goes into is a sacrament to me.’
Obviously, this somewhat extreme example of piety reflects a fanatical sense of Christian dedication, but you’ve got to avoid the temptation of jumping on the anti-Christian outrage wagon to get your head around this particular story.
That said, there there are plenty of other valid reasons to be annoyed with Christian (and Wicca and Pagan and etc. etc.) interpretations of ancient Irish culture.
Certainly, too many to cover here.