Boston has puddle radar.
He can be walking in a football sized parking lot and walk right through the only puddle.
If he sees one, he is compelled to jump right in it.
No matter if he's in church clothes or if he's sick or if there are man eating fish at the bottom, he'll jump right in. Had I not stopped him, he would have laid down for a swim in that muddy, dog pee puddle at the bottom of our driveway.