Using one refillable bottle keeps roughly 156 disposable plastic bottles out of the waste stream every single year.
Pick a bottle you enjoy using, because the one that feels good in your hand is the one you will actually carry.
Insulated steel keeps drinks cold for hours, while glass stays taste-neutral if you dislike any metal flavor.
Make it a habit by filling it each morning and keeping a spare at work, so a disposable bottle never feels necessary.
The planet keeps 156 bottles, and you keep the money you would have spent on them.