Depending on how dry your home is, it may need to be watered daily or even more often. Get into the habit of checking it when you get up and before you go to bed; if the end of the trunk dries out it will be unable to take up any more water. Never let the tree run completely out of water or you will need to trim 1/2" to 1" off the bottom of the trunk to get it to ever absorb water again. (If you purchase your tree pre-cut or if it has been more than a day since you cut it yourself, you need to take an inch off the bottom to get to a portion of the trunk where the tree can absorb water.)
You should cut off the base a little before you put it in water. Keep water in it at all times...actually I have read that most trees have been cut so long that they do not take up water. There is a product that claims it will help with the uptake of water....i do not remember the name however. I get a living tree now.