Place the diced potatoes and water into the stainless steel bowl of your Instant Pot. Secure the lid, close the pressure valve and press the Steam button. The display should read 10 minutes (high pressure). Allow the potatoes to cook. While the potatoes are cooking, mix the rest of the ingredients in a large bowl. Combine the mayo, mustard, onion, celery, salt, dill, vinegar, and pepper. Stir to combine. Quick release the pressure valve once the cycle is complete. Remove the lid once safe to do so. Drain the water from the potatoes (I used a fine mesh strainer) and dump them into the large bowl with the mayo mixture. Stir well to combine and sprinkle a little paprika on top if desired.