The purist water ever? But it does give you the runs.
This is Mizu no Genso ???? (Elements of Water) from Japan. It costs $3 for 300ml which is about 5 times as much as normal bottled water but contains electrolyzed water containing only Hydrogen and oxygen. No minerals or other added content.
It can be purchased at pharmacies in Japan but apparently you need to be pretty close to the toilet when you consume it!