Previous Versions can be found here
Water Cooler is a unique card with an ability that works very similar to Kindness's Passive Effect, healing 2 HP to all of your monsters, including itself, at the end of your turn.
This makes Water Cooler a very good support card, but also a highly targeted one. And because of its 1 ATK, it's another card easily killed by Muffet's Pet and Madjick.
Because of this, it's a good idea to increase its ATK with cards like Strength and Aaron's Secret (in Bravery) or Snowdrake (in general).
It's useful in a Kindness Deck, as it will heal all monsters by 3 HP each turn. It's also useful as a counter against Perseverance Decks because its healing effect is greater than the damage of KR.