That's a good question. If you're planning on keeping your Christmas tree up for more than a week, you should water it regularly to keep it fresh and healthy. The exact amount of water will depend on the size of the tree and the environment in which it is placed, but typically, you should water the tree once every two to three days. Make sure to check the soil and ensure that it is moist but not soggy. If the soil is too dry, the tree could start to wilt or lose its needles, while too much water could cause it to rot or develop fungal growth.