It depends on what kind of bottle you have. Our Tritan (i.e., plastic) Chute, eddy+ and Podium bottles are safe to freeze—just make sure you only fill them ¾ full so there’s room for the water to expand.
If you’re using a bottle with a bite valve (like the eddy), you might want to remove the cap before putting it in the freezer—otherwise, you’ll have to wait for the ice in the straw to thaw before you can drink anything.
We don’t recommend freezing the stainless steel, glass or Groove bottles, though you can certainly fill them with ice cubes if you like your water extra cold.