Water conservation; 1 plant per person? Do we need to limit water per pot plant? Desalinization?!.

According to research, a cannabis plant consumes around 22.7l (or 6 gallons) of water per day during the growing season, which takes place from June to October.
In addition to drinking 1 gallon per day if every person had 1 pot plant. That 7 gallons of water per person per day. How quickly will we simply run out of water?