Combine the macaroni, 4 cups water and 1 tablespoon salt in an Instant Pot® (see Cook’s Note). Follow the manufacturer’s guide for locking the lid and preparing to cook. Set to pressure cook on high for 4 minutes.After the pressure cook cycle is complete follow the manufacturer’s guide for quick release and wait until the quick release cycle is complete. Careful of any remaining steam, unlock and remove the lid and switch to low saute setting. Stir in the evaporated milk, butter and 1/4 cup water. Then add the Cheddar, a little at time, while constantly stirring, until the cheese is completely melted. Serve hot.