The best thing to put in the water is a tree preservative, which helps keep the tree hydrated and healthy throughout the holiday season. You can find tree preservatives at most garden stores or online. The preservative helps prevent the tree from drying out and dropping needles too quickly. It also helps keep the water in the stand clear and clean, which makes it easier to keep the tree looking fresh. Additionally, you can use a tree skirt to catch any stray needles and keep the floor clean.