Place the chicken and the water in the insert of a 6-quart Instant Pot or pressure cooker and sprinkle with the kosher salt and peppercorns.
Select High Pressure and set the timer for 10 minutes. When the timer sounds, use the Natural Pressure release, and allow the valve to drop and carefully remove the lid.
Remove the chicken from the Instant Pot and shred, dice, or slice. Serve hot or chill to use for later.
Like any pressure cooker recipe, allow extra time for the pressure cooker to come up to temperature. This typically takes about 5 to 7 minutes, but depending on the thickness of your chicken breasts and how many you stack in the insert, it could take longer. I don't have the exact time for this since each of you are different, so you will have to play with it.