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.

Sources:
https://www.c40.org/case_studies/the-...
https://www.verkis.com/projects/utili...
https://nea.is/geothermal/direct-util...
https://icelandmag.is/article/nine-fa...
https://askjaenergy.com/iceland-renew...
https://nautholsvik.is/en/
https://perlan.is/about-perlan/
https://www.epa.gov/coalash/coal-ash-...

Research on Blue Lagoon and a skin condition: https://doi.org/10.1016/S0738-081X(96...

Filmed safely: https://www.tomscott.com/safe/

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