I use the PET freebies from supermarket bottled water. An empty two litre container weighs about 40 grammes, that's very much lighter than a typical metal bottle. (A full 2 litre PET bottle weighs about 2040 grammes of course.) Most of the time I'm on a motorcycle, and I carry three or four full bottles. Usually a couple of sparkling ones because I prefer it to drink straight, and a couple that I've filled from a tap or wherever for my tea and cooking. I usually carry two or three empty ones too, crushed flat. Every now and then one of them will spring a leak so I either make a funnel or wide-mouthed container with it, or I throw it away.
I have a number of Sigg and Sigg-type water bottles but nowadays they mostly have fuels in them. In that case the stoppers need to be fuel proof. A lot of the ones sold with water bottles aren't. Some fuels make them swell, then they don't really fit the bottle any more and the threads get damaged or destroyed.
I'd be reluctant to use bottles such as bleach bottles which are not designed/sold for use in contact with foodstuffs. There are concerns about harmful chemicals which may leach out of the container into the water. I'd have no such qualms about metal containers as long as they weren't coated on the inside with something unfit for food contact and they were cleaned well enough, but bare mild steel would inevitably rust. Bare aluminium should be fine if you discount the suggestions about Alzheimer's although I've had a couple of aluminium containers develop serious corrosion when kept full for a long time.
