IMO, aluminum water containers (and cook pots) are fine. I suggest you take the alleged dementia hype with a huge dose of salt. Speaking of which, the only hesitation I have about scouts using a SIGG or other aluminum canteen is that most beverage powders have some citric acid / ascorbic acid in them. Aluminum can react with that.

Aluminum typically gains a protective oxide coating over time - otherwise we couldn't use it, as it's a fairly reactive metal. But it's almost an apples-oranges comparison to, say, drop shiny new aluminum foil in vinegar and erroneously extrapolate that a little orange beverage powder is going to dissolve your canteen - t'ain't so. But to be on the safe side, avoid putting acidic stuff in aluminum canteens - stick to water. Acidic beverage in aluminum canteens does get a little whang to it after a while, as any old former scout or GI can attest.

I think that HA-III (hard anodizing) finishes are pretty resistant to that sort of mild acid attack.

I remember/used surplus GI aluminum canteens - even preferentially carried one for a few years in Alaska (see discussion about thawing). I use an aluminum pot for melting ice/snow. Have / occasionally use other uncoated aluminum cookware. Use non-stick coated aluminum cookware on some backpacking trips. Absolutely love my GSI HA 12" dutch oven - more than my cast iron ones for 90% of my uses. I don't do stupid things with aluminum, but it's not measurably harmful.

What were we talking about... seriously, if you want to use aluminum canteens, there's nothing particularly dangerous about that. Use common sense and don't leave it full of V8 juice for a week. And remember to loosen/remove cap before thawing out a frozen one on a stove... saw that once - fairly exciting moment inside the arctic tent...

Tom