Add water and 1 teaspoon salt to a 6-qt Instant Pot®. Place metal trivet into the pot. Gently add potatoes on top of the trivet.
Select manual setting; adjust pressure to high, and set time for 10 minutes. When finished cooking, quick-release pressure according to manufacturer’s directions.
Remove potatoes and trivet from the Instant Pot® and drain excess liquid before returning the potatoes to the pot. Stir in buttermilk, milk, sour cream, Ranch Seasoning and Salad Dressing Mix and butter.
Using a potato masher, mash potatoes until smooth. If the mixture is too thick, add more milk as needed until desired consistency is reached. Stir in chives; season with salt and pepper, to taste.