> I don't really understand why most if not all bottles don't use aluminum instead of plastic.

Because aluminium is a lot more expensive and difficult to manufacture at scale than plastic. It's also a lot more reusable, but reusing aluminium costs energy, and reusing glass bottles requires either energy to melt it, or an extensive recycling / reusing infrastructure (like with beer bottles over here).

Re: sparkling water, there's water fountains that can produce sparkling water on the fly now. Ask your employer to get those installed.

Something I know a boat load about. You are correct glass I would say is the worse for recycling (unless like you stated there's an infrastructure in place). At municipal recycling facilities (MRF) glass is the first to come off the recycling line. It gets smashed up and anything that is roughly 3inches or smaller ends up in the glass, so a lot of contamination.

Aluminum is easier to recycle, but you cannot melt down cans (UBC's) back into cans without blending metals as they consist of two different aluminum (the top and the body). If the cans are completely clean the big guys (alcan...) can melt them down. If there is any contamination it has to go to a secondary smelter which adds to the process.

Is there a reason why steel fell from favour for drinks cans?

Back in the 80s we did rudimentary recycling streaming in school with a magnet to separate steel and alu cans, but now they all seem to be alu.

Isn't aluminium supposed to be toxic? Probably the amount absorbed from drinking from aluminium bottles wouldn't be enough to cause concern, but I'm not sure I would risk drinking from them all the time.

Aluminum is one of the most abundant minerals on earth. It's probably in just about everything. You almost certainly get more from your anti-perspirant that you do from an aluminum can.

Is PTFE or PET any safer?

Water is not packaged in aluminum cans because of consumer views. Plastic is clear, so you can see the "clear, pure water" inside. Metal cans are more often associated with beer and soda, and there's the distant association of metals with a metallic taste (something that doesn't happen as all aluminum cans are epoxy-lined to prevent corrosion). Some sparkling water is still packaged in aluminum cans, but the vast majority choose not to.

Paper is probably the most ecologically friendly water packaging, followed by glass.

Perrier does come in cans.