For a Christmas tree, water is usually added to the base of the tree to keep it fresh and hydrated. The amount of water needed depends on the size of the tree, but a general rule of thumb is to make sure the water level reaches at least an inch above the bottom of the trunk. Water can be added by using a watering can or by simply pouring it into the tree stand. It's important to keep the water level consistent throughout the holidays, as a dry tree can become a fire hazard.