Add the water to the bowl of the Instant Pot. Squeeze the juice of 1/2 lemon into water.
Add the Instant Pot trivet. Place the salmon fillets on the trivet.
Cook on High Pressure for 5 minutes (frozen) or 3 minutes (fresh): Press the Pressure Cook button, making sure the “High Pressure” setting is selected, and set the time. Note that it takes about 5 minutes for the pot to “preheat” and come up to pressure before it starts cooking. (During cooking, avoid touching the metal part of the lid.)
Quick release: Vent the remaining steam from the Instant Pot by moving the pressure release handle to “Venting”, covering your hand with a towel or hot pad. Never put your hands or face near the vent when releasing steam. Open the pressure cooker lid.