Buko Onsen of Chichibu,Saitama

N.B. All of my onsen pics are watermarked all the way through.

This is a picture of one of my very favorite hot springs in Saitama Prefecture in Chichibu.
The alkalinity in this water is rated at 10 pH !

What does that mean, exactly...?

pH (lower case "P" upper case "H" potential of Hydrogen) is the measure of alkalinity and acidity in water on a scale of 1 to 10. Drinking water is typically measured at around 7 pH.

Lower numbers denote higher acidity levels whereas higher numbers denote a higher alkalinity level.
The higher the pH the more beneficial it is for the skin. Natural skin emollient !