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These are the ubiquitous water bottles you'll find in many a hiker and backpacker's pack - sized at one liter (that's a hair over a quart for us non-metric folks) - they are a good compromise in size and capacity for shorter distances between water sources or as a supplement to a larger water container, like one of our 3-liter bladders. Yes, they are well cleaned after every use, with a light bleach solution, so they're as safe as the mug at your local diner.
The ones we rent are the nicer ones - no BPA and an easy screw-top wide-mouth lid. The main advantage over bladders with a drink tube is that it's simply easier to drink from - it's faster and your get more volume at a shot. And they are better for added powder mixes or ice. A disadvantage is they are heavier and take up the same amount of space whether full or empty. And you'd need to carry several of them in areas where water could be scarce between stops.
These are about 3.5" in diameter and 8" tall. Each weighs about 6 ounces.