The comments interest me about backflushing.  I have been of the opinion that the danger of ingesting "nasties" is not a question of do you prevent all of them but can you keep their numbers below a certain threshold.  I think of what I might get in my system by swimming in water that is "reasonable" but not up to drinking quality.  I suspect most of us do not think twice about taking a swim, certainly we are exposing ourselves to nasties when we do that.

With that in mind, what is the issue with backflushing using water that is "swimmable" (for those especially concern, a minimal forward flush with "debugged" water could be added)?  Just asking the question, for those more expert in these matters than I.