I water my xmas tree but the needles still keep falling off like heavy rain. What do I do?

"It's probably too late for that one" ... but, 

Recutting the stem on the Christmas tree

When caring for a live Christmas tree, remember a Christmas tree is essentially a giant cut flower. Unless you cut your own Christmas tree, chances are the tree you buy has been sitting on the lot for several days, possibly weeks. The vascular system that draws water up into the Christmas tree will have clogged. Cutting off just a ¼ inch of the bottom of the trunk will remove the clogs and open up the vascular system again. You can cut more off, if you need to for height reasons.

Source:  https://www.gardeningknowhow.com/ornamental/trees/christmas-trees/make-christmas-tree-last-longer.htm

Do what Alf said. and what my parents did. Mom always added a little bit of white syrup to the water she used. She said it acted like natural sap.