Heat oil in a stockpot or large saucepan over medium-high heat. Add the onion, leek, swede, carrot and celery and cook, stirring, for 5 minutes or until brown.
Add the water, parsley, peppercorns and bay leaves and bring to the boil Reduce heat to low. Simmer, uncovered, for 2 hours, skimming the top every 30 minutes.
Remove from the heat and pass the stock through a fine sieve/strainer. Discard solids. Allow to cool, then refrigerate.