I will not drink water from a disposable plastic bottle.
It won't be hard to find them. I imagine the conference organizers will provide them by the bushel.
But remember: every piece of plastic you consume will haunt the planet for hundreds, probably thousands of years.
The worst thing to use plastic for is something disposable.
And bottled water? Much of it is not even cleaner or "better" than tap water (though it will almost certainly have filtered out the nasty chlorine taste). Much of it is actually nothing more than filtered tap water (for example, Dasani-Coke).
Instead, bring a steel water bottle (best not to drink or eat out of plastic altogether - there are many inexpensive such bottles available via Amazon and so forth). Refill it as needed.
If lots of us foreswore plastic water bottles at Kscope15, we could reduce landfill and waste by hundreds of bottles. ODTUG would likely even save some money.
And if you forget or can't get hold of a reusable water bottle, no worries! Drink the water from your first and only disposable plastic bottle - and then reuse it for the rest of the conference!
On behalf of Planet Earth and all of its inhabitants, I thank you!