I ensure my little boy uses only metal water bottles.
I ensure my little boy uses only metal water bottles.
Aluminium bottles are always coated with plastic in the factory, which flakes off and usually isn't really better than plastic-bottle-plastic, sometimes even worse (containing PTFE, BPA, ...). As soon as the coating is gone, aluminium will dissolve in the water, and aluminium salts are known to be "not good", in addition to the influence on taste. Same for copper, in addition to the hassle to keep copper clean. Steel bottles are better because proper kitchen-quality stainless steel (the one with Molybdenum in it, in addition to Chromium and Nickel) doesn't leech out into common drinks (including salty hot broth, which would stain CrNi steel) and doesn't need inner coating.
For storage, use glass bottles. The material of the seal is usually not a problem if there is no contact to the liquid and the seal doesn't crumble. When reusing bottles, make sure to only use fresh or at least good-looking caps. And sterilize things properly (taking into account what the seal is suitable for), because mold and bacteria are far more harmful than common metal or plastic contamination.
Also, corks promote microbiological contamination of various kinds, leading to e.g. the common failings in wine (there is actually a multitude of "cork" faults, not just one): https://en.wikipedia.org/wiki/Wine_fault
I'd prefer any metal or plastic to cork actually. Just because it is "natural" or "traditional" doesn't make it any good.
Given that almost all metal bottles are coated aluminum, the vast majority of "metal water bottle only" parents are doing more harm than good IMO.
First of all, at least where I live, tap water has chlorine. Which seems to carry some risks (see, e.g. https://pubmed.ncbi.nlm.nih.gov/12594192/).
Secondly, my building has copper and PVC pipes, which are also suspected of having some adverse health effects.
Thirdly, where I live, sometimes (about once per month) tap water comes out brown. Authorities typically say that it's fine to drink, and I suppose they analyze it and it conforms to some official standard, but I'm not going to drink or give anyone brown water. And that also makes me think that maybe the days it doesn't look brown to me, it might be also somewhat brown, just maybe not brown enough for me to notice.
Maybe I'm wrong and plastic from bottles is much worse than these things, but I don't think you should be so amazed that people can prefer bottled water. At the end of the day, it's a matter of picking your poison... with incomplete information.
If some of the contamination is "pre bottling" then the issue may be way more pervasive than just bottled water.