Definition: A temporary accumulation of water on the golf course. In other words, a lake is not casual water, but a puddle of rainwater (that will disappear once the sun comes out) is.
Casual water must be identifiable before or after a player has taken his stance. Ground that is merely wet, spongy, mushy or muddy is not casual water. There must be an accumulation of water above ground that is visible.
Dew and frost are not casual water; snow and natural ice can be casual water or loose impediments, at the player's discretion; manufactured ice is an obstruction.
Rule 25 covers relief from casual water.
