For a Christmas tree, the water temperature should be around 70 degrees Fahrenheit. This will help the tree to stay hydrated and prevent the needles from drying out. It's important to keep the water level consistent and to change it every few days or so. If the water gets too low or becomes stagnant, it can cause bacteria growth and damage to the tree. It's also a good idea to keep the tree away from any sources of heat or drafts, as this can cause the needles to dry out more quickly.