OG, they brought that themself, and I think it's great foresight by them, but it is the festival staff's obligation to supply rinse water in some fashion.
At the Great Taste, there is a centralized dripping cow tank ( appropriately ) so if you want to rinse you can, but you have to walk a bit. Our system is more convenient, but I've never seen the problem with the way they do it in Madison.
Also, there was plenty of bottled water available for drinking. Why not grab a couple of those, rinse with it, and drink the rinse water out of your glass. Ambulatory rinse water.