1: even if it were a glass bottle you should regularly clean it with a bottlebrush because receptacles can develop mold, bacteria, or fungus if not cleaned properly. Sometimes it’s not visible to the naked eye

2: if it’s plastic, get rid of it. plastic bottles degrade quickly and are not meant to be reused. The long polymer molecules that plastic is made out of breaks up, and your water becomes increasingly contaminated with microplastics (broken polymers) as you reuse the container.