Pour the water or wine into an Instant Pot. Set the pot’s rack (with the handles up) or a large, open vegetable steamer inside the pot. Set the fillets skin-side down on the rack or in the steamer, arranging them so they overlap as little as possible (do not stack them). Set two barely overlapping lemon slices on each fillet. Sprinkle the fish and lemon slices evenly with the pepper and salt. Lock the lid onto the cooker.
Pressure cook on High pressure for 6 minutes with the Keep Warm setting off. The valve must be closed. For fresh salmon, pressure cook on high for 3-4 minutes, depending on thickness.
Use the quick-release method to bring the pot’s pressure back to normal. Unlatch the lid and open the cooker. Use a metal spatula to transfer the fillets one by one to serving plates.