Originally Posted by
gummibar
Thanks for the replies. I must say that I'm having blocked nose these days so I can't really smell any sulfur coming out of the onsen.. However the sulfur smell at Owakudani is strong enough for me to detect. Also I did not seem to notice any signs posted on the walls of HR Hakone Onsen to certify the water.. Maybe it's hidden in some corner but I didn't bother looking for it. Nonetheless, I enjoyed the onsen even though I found it a little too clear (which is not a bad thing). Typing this now while I'm waiting for the shuttle van to take us to Gora then on the way to Tokyo!
Natural onsen water can be filtered, supplementarily heated, reheated, and even mixed with a limited amount of non-onsen water at the individual facility and still be certified as natural onsen. So it is not uncommon for baths to seem different even between adjacent facilities, and at large onsen with multiple baths, even among the baths at the same facility. As hailstorm pointed out, there has to be a posted specification in a readily visible location. The bath at HR Hakone is natural onsen.