Tumble posted:

for me it always made sense. Mario lives in a pretty safe universe when you think about it; his worst enemy is Bowser and you can mess him up just by swinging him around by his tail. The fire Bowser breathes is just a couple of milder flames that dance around so he's not exactly a Game of Thrones level dragon, he's more on the level of a dinosaur Muppet.

It makes sense that going for a refreshing swim would get Mario back to normal and ready to go hop around some some more. Heck, I bet even the standing water pools don't have any harmful bacteria in them, Mario's probably guzzling that stuff down.