Ask EWG: I am looking for a safer (chemical free) option than plastic water bottles. Are stainless steel water bottles safe?
Answer: Stainless steel water bottles are the way to go, especially for hot liquids. Make sure your stainless steel bottle doesn't have a plastic liner inside, which may leach bisphenol-A (BPA), an industrial chemical linked to birth defects of the male and female reproductive systems and other health concerns.
If you do use plastic bottles or bottles with plastic linings, avoid using old or scratched ones, putting them in the dishwasher, and using them for hot liquids. Polypropylene bottles are a good alternative, slightly opaque/translucent with the #5 labeled on the bottom (as opposed to polycarbonate plastics, which are hard, see-thru plastic popularly made by brands such as Nalgene and Lexan).
Canned foods have actually been shown to be the predominant source of our exposure to bisphenol-A (from plastic lining inside). So along with switching bottle types, try to eat more fresh foods and use ceramic, glass, or unlined metal containers for storing and heating food.