You do not get relief simply because your ball comes to rest on ground that is very wet or spongy. An accumulation of water must be visible above ground.
Dew and frost are not casual water; snow and natural ice (other than frost) can be casual water or loose impediments, at the player's option. Ice cubes or other manufactured ice is considered an obstruction.
See Rule 25 (Abnormal Ground Conditions) for more on casual water.

