Please Don't Drink Out of Plastic
This is a reply to Roy Tang because I liked his blog post (he is the opposite of me, I carry EVERYTHING, maybe I will do a similar post since I need to reorder my bag(s)) but also had a momentary please don't at that plastic water bottle.
For context: I am a chemist who has worked in toxicology and contaminant testing my whole career.
It's not about the BPA - though certain plastics do carry that risk. It's not about microplastics (though I trust microplastics to be safe about as much as I trust asbestos to be safe).
It's about bacteria.
On a general level, you should wash your water bottle every other day, every three days at most. But plastic even more so.
Plastic microdeteriorates- it doesn't look deteriorated until it goes yellow, or starts to disfigure. But even when it looks fine, it generally has a whole bunch of microcracking going on in there. Sun makes this much worse - plastic degrades faster with UV light - and sometimes plastic degrades faster just because it's exposed to water, so any tiny piece that wants to work free has both force (from water movement) and a fun chemical pull from the polarized nature of the water molecule.
So you've got a real uneven surface in there. And you can't wash it at bacteria-killing levels of heat, or it just melts. What happens? Bacteria.
Every time you drink, bacteria from your mouth, breath, and environment get a nice fun ride straight into a nice, contained, warm environment (I'm assuming the bag stays with you, so indoors a fair amount of the time, and generally close to your nice warm body acting like a space heater).
Bacteria are gonna love that. Especially when it also means miniscule pieces of food from your backwash, and a dark environment in your bag.
Bacteria also can go into a hibernation stage, where they basically put themselves in a chemical cocoon and stasis until things get nice again. That's why unless you go real cold, you don't kill bacteria in a freezer. You just pause them, and your food will go bad if you take it out and let it thaw, even if you never open the container.
And not only that, but they like to form microfilms, which are really hard to remove from surfaces, even with a bottle brush (and that brush is just scraping those interior walls to make more homes for the bacteria once it leaves).
Basically? A lot of people get food poisoning and blame it on their last meal or an odd tummyache, but it isn't. It's their water bottle. (Or the water tank in their coffee machine, or-)
Please get 3 steel bottles, and rotate cleaning them. They can go in the dishwasher. You can shove detergents in them. You can even bleach them. And you have far less likelihood of getting bacterial gutache.
Thanks, Your friendly neighborhood scientist