Cut your carrots and parsnips into pieces that are roughly the same size. Add them to your Instant Pot along with the water.
Close the Instant Pot's lid and set the valve on "sealing". Cook on high pressure for 2 minutes (3 minutes if you want them really soft or you're using particularly large carrots & parsnips). It'll take about 10 minutes for the Instant Pot to come to pressure.
Once the countdown has finished, carefully do a manual pressure release. Take the lid off as soon as it's done (or the veggies will continue cooking), and take the insert out and carefully discard the water (leave the veggies in the insert).
Put the insert back into the Instant Pot and add in the butter. I set the lid back on top for about a minute to help the butter melt. Add the salt & pepper and parsley and gently toss to coat. Transfer veggies to a serving bowl.
Inactive time represents the time it will take to get your Instant Pot up to pressure.