Saint Patrick prayed 150 psalms in water for penance.  Saint Patrick prayed, fasted and worked all day.

Hmm...although much of what is told about Patrick is legendary and his own writings consist only of the very brief Confessio and Epistola, I tend to believe that he he did engage in this penance with frigid water. I do however wonder if he prayed 150 psalms or if he prayed 151 psalms since not all manuscripts in his time had yet isolated Psalm 151 to an appendixed position apart from what the Roman Church now regards to be the canonical psalms.