Although it is very common to see shower systems built "on the ground" with an evaporation pond as part of the system, those maintaining it are taking a chance that all the grey water will evaporate. Figuring one shower is 2-4 gallons, that is a LOT of water if you have even three people using it. I've seen such on the ground systems with an evaporation pond the size of a piece of plywood: for sure a fail.
One solution is to raise up the "platform" and collect the greywater in 5 gallon buckets that ARE the very structure that is elevating the shower platform. Caretaker of shower system can then reduce time maintaining system as it will handle about 14 gallons before need to transfer greywater to containers or evaporators.
Although I've posted some of the "how to do it" instructional pictures before, I've added more:http://goo.gl/1qusQ