Peel the sweet potatoes and chop them into cubes. Add the water to your instant pot and place the trivet or a steamer basket inside. Add the sweet potatoes and spread them out evenly.
Place the lid on the instant pot and set the valve to sealing. Then turn on the Instant Pot to high pressure (manual) and cook for 10 minutes.
Once the sweet potatoes have cooked, carefully flip the valve open to quick release the pressure. Open the lid, remove the steamer basket, and drain the potatoes.
Add the melted butter to the Instant Pot. Return the drained potatoes to the pot, and add the brown sugar, cinnamon, salt, and nutmeg.
Mash everything together with a potato masher until the butter, sugar, and spices are mixed in and the sweet potatoes are smooth. Serve warm.