If it is white glutinous corn, usually after the water boils to cook for more than 15-20 minutes, or even longer; yellow corn is more difficult to cook, the ordinary pot is usually enough to cook it for at least half an hour.
As for how much water to cook corn, no matter what type of corn belongs to what type of varieties of corn, water more than corn can be, never put too much or too little, that is not appropriate!