2Sam 23:16

“And that even the drinking of cold water with lust is reprehensible David, the wise man of God, shall prove unto thee, for when he lusted to drink water from the great cistern which was in Bethlehem, and those who did hear him obeyed and brought it to him, he suppressed his lust, and poured it out before the Lord, as if by means thereof he was pouring out his lust; now the nature of water is not such as to cause sin even if he had partaken thereof, for it is cool and pleasant, but he perceived within himself that he had asked for it with lust and he conquered his lust, and did not grant its request. And he did this also that he might vex those who had been ministers unto his lust, by turning back their kindness upon themselves, that he might teach every man not to be in subjection unto his lust, and that we should not make our faces joyful towards those who minister unto our lust.”

“When long afterward David sat against the battle lines of enemies, he wished from desire to drink water from the cistern of Bethlehem. His chosen soldiers, breaking through the midst of the opposing forces, brought back unharmed the water the king had desired. But the man instructed by scourges immediately reproached himself for having desired water at the peril of his soldiers, and pouring it out, he offered it to the Lord, as it is written there: He poured it out to the Lord. For the water poured out was turned into a sacrifice to the Lord, because he slew the fault of concupiscence through the penance of his self-reproach. He therefore who once did not at all fear to covet another's wife, afterward was even afraid because he had coveted water. For since he remembered having perpetrated unlawful things, now stern against himself, he abstained even from lawful things. Thus, thus do we do penance, if we perfectly bewail what we have committed.”