Cut the potatoes into quarters approximately the same size. This will ensure even cooking.
Place the potatoes in the Instant Pot or pressure cooker and add the water. Season with salt.
Lock the lid in place and cook on high pressure for 10 minutes. Allow the pressure to release naturally....do not release it manually.
Add the butter, milk, salt and pepper to the pot and mash using a potato masher.
Transfer the mashed potatoes to a serving bowl and serve immediately.
Notes
Mashed Potatoes can be made up to 2 days in advance and stored in an airtight container in the refrigerator.To reheat, warm over low heat in a saucepan or return to the Instant Pot and heat on the warming function.