Water damage is a peril that a standard homeowners insurance policy may cover under dwelling coverage. However, the cause should be a covered peril.
Some perils, like sewer backup or hidden water damage, are usually only covered through endorsements.
Don’t confuse flood as part of water damage because it is almost never covered by homeowners insurance unless it was caused by a covered peril. To be fully protected from flood water damage, you must have flood insurance or difference in condition (DIC) insurance. These are separate policies, and very few insurers offer them.