This has been proven categorically time and again outside of China, thanks to the less than stringent quality control standards of governing agencies like the FDA, who for example classify bottled water as a food. Water treatment plants are required to keep constant monitoring 24/7, while bottled water companies provide only sporadic assay of water, and the requirement level of testing of tap water (to international/European standards) far surpasses the assay guidelines for bottled water. Distillation removes almost all contaminants, so is always preferable to ‘Spring’ or ‘Natural Mineral’ water, but again the QC of these companies is not under the same scrutiny.
Air is definitely the big one in Chengdu currently, I’m seeing the pollutant index above 200 almost daily, edging up past 250 frequently. That’s not getting any better any time soon, and I’m seriously considering an air filtration system in my apartment at the moment. Either that, or relocation. We are all of us sucking in heavy metals right now, and some of them will not be leaving your body any time soon. This is something I’d advise everyone to give serious consideration to while living here.