Watering a live Christmas tree is a delicate balance. You want to make sure the tree has enough water to stay healthy, but not so much that it causes root rot. The best way to do this is to use a watering can with a fine nozzle, and slowly pour the water directly into the soil around the tree, allowing it to absorb the water. Make sure to check the soil regularly to ensure it's not too dry or too wet. A good rule of thumb is to water the tree once a week, but more frequently if it's a hot day.