I have been using water bottle cages so long that its hard to imagine not having one. I think it certainly beats a bottle sloshing around in a waist pack. I did see once a Touring Rider that had a 2 liter bottle of water in his handle bar panner and a hose to sip from when ridding...
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No matter where you're at... There you are... Δf:=f(1/2)-f(-1/2)