There are many types of
water bottles and it pays to know which ones can be reused. A
bottle labeled 1 is only safe for a single use. When exposed to
oxygen or high temperatures, including sun heat, such a bottle
will discharge toxic substances that get into the water. Also
avoid bottles labeled 3, 6, or 7 as they exude toxic chemicals
able to penetrate drinks, and lengthy exposure can result in
severe health problems.
Bottles made of polyethylene (2 and 4) and polypropylene (5) are
suitable for multiple uses. They are relatively safe if you only
store cold water in them and regularly disinfect them.