The water for your Christmas tree should be cool and clean. Avoid using hot water as it can damage the tree's needles. You can use tap water or distilled water. If you choose to use tap water, it's best to let it sit out for a few hours before adding it to the tree stand to allow any chlorine or other chemicals to dissipate. Make sure to keep an eye on the water level in the tree stand and add more as needed. It's also important to keep the stand filled with water throughout the holiday season to ensure the tree stays hydrated.