If you were thirsty and I hand you a glass of water, you would be pretty sick if I gave you fresh water from my septic field rather than fresh water from my tap; the same goes for your well. Although we don’t always get to choose water with zero microbes for our frac, that doesn’t mean we need to (or should) blindly accept using what’s available. Every water is different and has a different microbial community. Two waters could have the exact same number of microbes: one source has all harmless, non-threatening microbes, and the other has all microbes capable of well-souring. Ideally, given the choice, you wouldn’t frac with the souring-related microbes (sewage) and would choose the harmless microbes (tap water), but at least by knowing the microbial threats in each source you can adjust your biocide treatment program accordingly.