Water Absorb (the ability) has two problems:
1. When your pokémon, that has Water Absorb, has full HP, and a water move hits your pokémon, nothing happens, not even an advice that says, the pokémon absorbed the damage but it's allready full of HP or something.
2. It "works" with the water status moves, like "Rain Dance" or "Water Ring", the move lose their effect (like recover the user, or change the weather to rainy) and recovers the pokémon with Water Absorb.
1. When your pokémon, that has Water Absorb, has full HP, and a water move hits your pokémon, nothing happens, not even an advice that says, the pokémon absorbed the damage but it's allready full of HP or something.
2. It "works" with the water status moves, like "Rain Dance" or "Water Ring", the move lose their effect (like recover the user, or change the weather to rainy) and recovers the pokémon with Water Absorb.