Ever noticed that water tends to symbolize transformation? Think about being baptized in church, jumping into a lake, or standing outside during a thunderstorm—these all indicate a fresh start or some sort of transformative power.
Want a specific example? How about the dramatic storm at the end of The Shawshank Redemption? After being accused of murder and spending decades in jail, the main character escapes from jail and is cleansed by a downpour. Not only does the rain wash off all the gunk that Andy acquired while squirming through the prison's sewer system, it also washes away his sins and identity as a prisoner. Yep, the water symbolically transforms him into a free, innocent man.
In Actaeon 's case, the water doesn't come from the heavens, but from Artemis's pond. She splashes him in the face, and the magical water changes Actaeon from a prideful, possibly sinful man to a sweet, innocent deer. It's like The Shawshank Redemption, but with hooves.