Sure that cast iron Christmas tree stand may look nice while it holds your tree upright but, unless you keep the water supply inside of it full, your tree will end up drying out. It is essential that your tree has an adequate amount of water at all times or you might as well drag it to the curb. Fill up the water reservoir in your stand and keep it full.
If you let the water level to fall so low that it allows the trunk to be exposed to air. Once the trunk meets the air it will seal over, which will prevent it from being able to take in more water. In other words, if you neglect the tree and add water later, the quick fix won't do you any good.