We learned about this in grade 10 science class. You'll lose a layer of skin.
This is about as calm as MSDSs get, note that it doesn't have any warnings about...anything really.
Besides which, I've drunk a small cup of it. No ill effects except it just tastes bad.
I think youtuber pranked you.
Pure Water Can Kill You http://isciencemag.co.uk/features/fact-of-the-day-1/
As with everything, the dosage is important and the article doesn't mention it being any different than normal water.
Here is a WHO report, off that you can jump to animal studies etc etc etc
https://www.who.int/water_sanitation_health/dwq/nutrientscha...
Maybe some of the minerals in water are good for you, and there's things around satiety.... But since all water is different it's only if you are really poor might this might matter. You should not be relying on random water for your micro-nutrients.
OK, don't do it for 20 years without more research, but it will not burn you. I don't know what The Action Lab did, but here's National Geographic doing it in a professional lab https://www.youtube.com/watch?v=hMh1lyeNsPc