Glass bottles are definitely safe as glass is a safe material to keep reusing and does not release toxins. Plastic bottles made of BPA-free material are safe to use and do not release toxins, these bottles can be reused over and over again.
How to care for your bottles to make them last longer?
Wash your bottles with warm soapy water to remove all kinds of residue on them. Leave them to air dry with the spout facing downward. Allow them to dry completely before replacing the lid and storing them away.