Sorry, I didn't realize you were talking about racing.The Bottleport sure looks cool, but if you bothered to read the thread 49208 linked to, you would know it's illegal. The company that's selling it once again has no idea what is allowed in the class and what isn't.
And btw, I use a piece of elastic that runs through the toestrap fittings at the back of the cockpit, with a bowline at each end.
Or better still, go sail a class of boat where it doesn't matter what you do or maybe take up an activity where you're not competing against anyone.Label me a cheater if you want but......unless your in the top tier of national and world domination just do what you need and what you find easy to use for your water bottle. Who cares if it's legal. It's just water.