In A Dutch Oven Or Soup Kettle, Saute Onion In Butter. Add Water And Bring To A Boil. Add Potatoes; Cook For 10 Minutes. Add Fish And Lemon Juice; Reduce Heat And Simmer For 10 Minutes. Add Milk, Evaporated Milk, Salt And Pepper. Garnish With Parsley And Serve Piping-Hot.