Put the bacon, onion, thyme and water in a pressure cooker and attach the lid. Set the pot over medium-high heat. When it begins to hiss, reduce the heat to medium-low and cook for 20 minutes. If the pot is not hissing, raise the temperature slightly until it does.
Remove the pressure cooker from the heat and let stand until the pressure subsides before removing the lid.
Transfer the bacon to a plate and let cool to room temperature (discard the cooking liquid). Wrap tightly in the plastic wrap and refrigerate for up to 1 week. Cut to the desired thickness to serve.