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.