Since we all know how bad disposable water bottles are for the environment (since most of them end up in landfills because they don't get recycled), it's a great idea to use a reusable water bottle. Both Nalgene and SIGG bottles are great, but if your goal is to stay hydrated during some kind of strenuous activity, lugging around a hard bottle can be kind of annoying.
Check out these bottles made by a company called Platypus®. Their water bottles and carriers come in a range of sizes and shapes, and they're all collapsible, "taste-free," lightweight, easy to fill, and rugged enough to handle temperatures from freezing to boiling.
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These are similar to Camelbak hydration packs, but more versatile. You can use Platypus bottles on their own or add accessories to them. I love the Neoprene insulted bottle holder to keep liquids hot or cold. You can also get a hands-free drink tube so you can tuck the bottle in any existing pack you're carrying and attach the tube to your shoulder strap.
These are perfect for hiking, biking, and backpacking because once the bottle is empty, it collapses so you can roll it up for easy, compact storage. Plus these are really inexpensive - an 80 oz bottle is only $9.95. You can check out all the Platypus gear at REI.com.