Another note about septic sytems and this is geared more towards large quantities, but still may have an affect on smaller more frequent quantities too. But If your leech field is under anything you want to grow on top of it you may want to rethink putting SW in your system. The salt run off into the leech field can kill anything it saturates. And if your septic system is made out of concrete, salt eats away concrete, so that my have an effect too at some point.