If you buy something like a Sigg aluminium bottle or no-name copy it will be lined with some kind of plastic.

If you use a light weight drinking bladder that will be plastic too. I've read that risk is much higher if you apply heat to a plastic container. This is why you should avoid microwaving in plastic containers.

So that leaves you either only using a cold liquids in plastic and accepting some risk or buying expensive (and relatively heavy) titanium drinking bottles.