Actually, the water needed for the meal heater is less than a tablespoon, and from experience I can promise you that the stuff you wouldn't even dare drink after boiling it and adding clorox will heat a meal nicely to non-glueyness.
Just don't use Pi--. I made that mistake, thinking "Well, it is still pretty much still water." Yes, it did heat the meal, and yes; it tasted like... And I still had to eat it. Had to throw away the heater, too.
After that experience, larvae and salamanders were quite tasty!