I just adapted a Cornelius keg for water storage. For a quick test, I pressurized it to about 15PSI and it works great. I would expect this will be great for washing stuff, spraying off bikes/kids/whatever, and drinking water.
I am going to pair this up with my ARB air compressor for camp use. My plan is to use the air compressor setting for max pressure so I don't need a regulator on the keg itself. I am shopping for fittings to make it useful around camp (on/off valve, sprayer head, fittings for charging it).
I'll post up pics when I get it working (or not working). Thanks for the idea all!