Pour the water in the bottom of your pressure cooker and set in the steamer insert (I use one of those vegetable steamers that looks like a little flying saucer when its closed).
Arrange the corn in the steamer basket- I can only fit 3 ears of corn in my 5 qt cooker with the basket in place. If you have a larger cooker you can increase the amount of corn you cook, and can up the water to 1 1/2 cups.
Secure the lid and seal. When the cooker comes up to high pressure (15 psi), set a timer for 2 minutes. After the 2 minutes are up, run the cooker under cold water until it releases.