1. In a large saucepan, heat oil over medium heat. Add onion, celery, carrots, garlic, and salt and cook, covered, stirring occasionally, until slightly softened, about 5 minutes. Add 8 cups water, parsley, and bay leaf. Bring to a boil. Reduce heat to medium-low and simmer, uncovered, for 1 hour.

2. Strain stock through a fine-mesh sieve placed over large bowl. Gently press the solids with a rubber spatula or back of a large spoon to squeeze out juices. Discard solids.

3. Use stock as is, or for a more concentrated flavor, boil to reduce by one quarter to one half.