Your reusable bottle choice comes down to personal philosophy: how much risk and what types of risk are acceptable to you? If experts don’t agree, do you need proof that something is safe before you use it (this is the precautionary approach), or do you need proof that something is unhealthy before you decide to avoid it?
Most disposable water bottles are made of plastic #1 or PET. Some people try to reduce their plastic use by washing them out and reusing them, but plastic #1 is not meant to be reused due to the possibility of bacterial buildup. A Canadian study found that 13% of the water bottles tested in an elementary school had bacterial levels (9% were found to have fecal coliforms) exceeding drinking water quality guidelines by the end of the school day. Unfortunately, children sometimes don’t wash their hands thoroughly before opening them. These bottles are not durable enough to withstand use, cleaning, and reuse without losing their integrity. The compelling issue with these bottles is not whether plasticizers leach into the drinks, but that bacteria accumulate in them and cannot be easily washed out. Long storage time on the shelf or in a warm garage or trunk increases the likelihood of bacterial growth and concentration of antimony in the water. Contrary to urban legend, freezing bottled water has not been shown to cause any degradation of water quality.
Plastic #3, #6, and #7
Many sources say not to drink from plastics 3 and 6 due to the potential for leaching. Plastic #3 (PVC) can leach phthalates which have been shown to cause developmental and reproductive damage. Plastic #6 (polystyrene) may leach styrene which can cause nervous system effects and liver damage. Polycarbonate, one type of plastic #7 (other assorted types) from which the clear, brightly colored bottles are sometimes made, has been shown to leach Bisphenol A (BPA), a hormone disruptor that mimics estrogen. Experts agree that Bisphenol A can leach into the drinks at low levels. One group of researchers said the levels were too low to cause any concern, and another said that the levels were significant. Read this Q&A on BPA and Plastics from the Johns Hopkins Bloomberg School of Public Health to learn more. BPA has been banned by the Canadian government.
Plastics #2, #4, and #5
Plastics #2, 4, and 5 are the healthiest plastic bottle options since they are not known to leach. These plastic bottles do absorb odors and stains and many of them leak if not held upright. This lack of durability makes them a poor choice for long term use. Plastic #2 is commonly recyclable, whereas plastics #4 and 5 are not recyclable in most municipalities.
Aluminum is reactive with acidic liquids so these bottles have to be lined with a layer that could become a problem with wear and tear. Some liners contain BPA, the hormone disruptor, including ones used in the most popular aluminum bottles (Sigg). Sigg bottles also have very narrow necks that make them difficult to clean, dry, and load with ice.
Food-grade stainless steel does not have any known safety issues and is non-reactive so the bottles do not leach and do not have to be lined. These single layer lightweight stainless steel water bottles appear to be the best choice health-wise.