Melt Parkay in large saucepan over medium-high heat; add onion and celery. Cook 3 to 5 minutes or until vegetables are tender, stirring occasionally. Add flour; cook and stir until vegetables are coated.
Add potatoes, milk, water, salt and pepper to saucepan; stir to combine. Bring mixture to a boil; reduce heat and simmer 10 to 15 minutes or until potatoes are tender and soup thickens.