Drinking mineral water was not so usual till 90s. Although there were large 1.5 liter pet bottles sold at stores, no beverage company sold Japanese mineral waters in 0.5 liter pet bottles. Which means it was impossible to buy mineral water from vending machines. Green tea sold at vending machine was much earlier than selling mineral water. Therefore mineral water sold in 0.5 liter bottles were imported, such as Evian or Vittel.
Japanese thought that water is free and it is not a worth to pay for it, especially if you are thirsty. Also Japanese preferred to bring green tea rather than water for hiking or trekking. However, the custom has changed and mineral water are sold everywhere including at vending machines.
Mineral water in Japan used to be branded as water source located in mountain area. Famous mineral water are Rokko no oishii mizu; Tasty water of Mt.Rokko or Minami Alps no tennen-sui; Natural water of Southern Japanese Alps.
I have encountered to interesting mineral water last month. It is called Uchu no tanemizu - Space water. Of course water is not produced in space but this mineral water is drunk by astronauts in International Space Station. The water source is located in Tanegashima island, which is located south of Kyushu and delivered to ISS by Japanese automated cargo spacecraft called Konotori, which is launched from Tanegashima Space Center.
The quality is approved by NASA and could be bought only in Japan at selected stores. Although becoming an astronaut is quite difficult, drinking mineral water which astronauts drink is quite simple.