All four Sam's events we did in the last 2 years had central water from a spigot, but 20 amps of power delivered to your site. We have buckets with us anyway, so not big deal to grab a shopping cart and fill 'em with water for dish washing. (No shopping carts at the finals, but nobody that made it to Bentonville was bitching about that. :becky
If you want water pressure in your trailer for an event with no hose feeds, consider using an RV water pump to feed water from buckets to your trailer. They will cycle on/off automatically. They run about 60 bucks:
[ame="http://www.amazon.com/Flojet-03526-144A-Diaphragm-Automatic/dp/B002P33KVQ/ref=sr_1_4?ie=UTF8&qid=1356243398&sr=8-4&keywords=rv+pump"]Flojet 03526 144A Triplex Diaphragm 3526 Series Automatic Water System Pump : Amazon.com : Automotive[/ame]
They make a garden hose adapter for it [ame="http://www.amazon.com/Flojet-20381-007-Quad-Port-Fitting/dp/B002UC8SUU/ref=sr_1_1?s=automotive&ie=UTF8&qid=1356245292&sr=1-1&keywords=flojet+20381007"]Flojet 20381-007 Quad Port Fitting : Amazon.com : Automotive[/ame] and I would recommend using one of those wire inlet screens that fits in a garden hose on the intake side. Use a heavy duty hose so the pump vacuum doesn't collapse it.
If you need a 12v source: [ame="http://www.amazon.com/Schumacher-PC-6-120AC-Power-Converter/dp/B0012BL8LG/ref=sr_1_2?ie=UTF8&qid=1356245713&sr=8-2&keywords=110v+to+12v+converter"]Amazon.com: Schumacher PC-6 120AC to 6A 12V DC Power Converter: Automotive[/ame]
So for about 80 bucks, you can rig your trailer to run at contests that don't have running water. Sam's isn't the only one, we have 2 other events we normally go to that have the same kind of setup.