The amount of water needed for a Christmas tree depends on several factors, including the size and species of the tree, the temperature and humidity in the room, and how long the tree will be displayed. As a general rule, a fresh cut tree should have the base trimmed 1/2 inch to 1 inch off before putting it in a stand and keeping it filled with water at all times. A smaller tree (less than 6 feet tall) will need about 1 quart of water per day, while a larger tree (over 6 feet tall) may need up to 2 quarts of water per day.