Normally, the answer would be no. But in these very limited circumstances, at Iceland's Blue Lagoon, you can swim in geothermal power plant wastewater, and it's even healthy: although the marketing material doesn't usually mention it. Here's a story about geothermal energy, cheap heat, and how to keep some ducks warm.
Research on Blue Lagoon and a skin condition: doi.org/10.1016/S0738-081X(96)00099-5
Filmed safely: www.tomscott.com/safe/
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