The steripen is UV light, so it won't leave anything else in your water. So if you are truly concerned, go for that option.

Me, I'm certain my tap water has *far* more chlorine in it than I will ever pick up backpacking - and note that the illinois study you reference is, while concerned with tap water, actually really concerned with public pools and/or hot tubs.

Public pools put in *buttloads* of chlorine - just see what happens when babies get taken into it.. it's also basically muriatic acid and bleach. - not the same as the Cl02 we use in backpacking land.

So me, I'm actually pretty happy with CL02 - foolproof. nothing to break, and it just works.

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