Joe: Your question does not address chlorides, which can build up under deposits, including bacterial deposits, resulting in pitting. The reduction of sulfur species in the water to hydrogen sulfide from sulfate reducing bacteria should not, in itself, compromise stainless steel. The real answer to your post is the effect of the quality of the water wrt 304/316SS. You have not adequately defined the water quality to permit an unqualified answer. However, there is much public information regarding materials of construction in waste water plants. Finally, the corrosion resistance of 316SS is generally superior to that of 304SS wrt pitting. Hope this helps! David Hendrix The Hendrix Group Inc.