For those of you who live near the coast or vacation there you're probably familiar with outdoor showers. Many beach houses have them so that you can wash off after a day at the beach without eventually clogging the drains indoors with a half a ton of sand. Obviously that's the main purpose, but to me nothing is more refreshing than taking a shower outside in the summer when the nights are not quite cool, but not hot either. I can also think of other benefits such as being able to jump right in and shower after getting dirty in the yard without tracking mud in the house, showering outside after being in the pool instead of running freezing through an air conditioned house to the bathroom, etc... Not to mention just having the convenience of another shower in your house at least a few months out of the year.
The question is, how to build one to code in a regular (ie: not vacation) home. Most of the ones I see at the shore just drain into the ground. They're built on a platform of pressure treated wood, and the water simply flows down through the gaps directly into the ground. This isn't a problem because A: none of the homes have basements, B: the water percolates quickly through the sand even in the wettest conditions, C: these homes are usually pretty old and built before any stringent codes that would provide guidelines for such a thing.
Here are my questions:
The water needs to go somewhere away from the foundation-would it be acceptable to simply pipe the water into a dry well like what you would use for downspouts, or would that not meet code since the water is "grey water."
Would Trex be the best material to build the partitions/roof/platform etc...with?
It is very difficult to answer your question because it depends greatly on where you live how that area treats grey water discharge. Here in Florida, and where I live locally, all black and grey water from plumbing fixtures must discharge into a plumbing system that will eventually carry it to a sewer line or into a septic tank; however, code allows exceptions to the rule with respect to grey water discharge where local authorities approve a particular grey water system (mainly for irrigation, brine discharge, etc.). I would start by calling your local heath department and then your local permitting office. They will most likely want to know where exactly the water is going, how deep into the ground it will be going, how much water, where your neighbors live, are there any fresh water lines or wells nearby, etc. My hunch is it that your shower should be allowed to drain into a properly built drywell. The only hinderance, I imagine, would be if your plan violates certain set back requirements. Good luck.