In a large saucepan, bring the water, potatoes, carrots, celery, onion, salt and pepper to a boil. Reduce heat; cover and simmer for 8-10 min. or until veggies are just tender. Remove from heat; DO NOT DRAIN. Meanwhile, in a medium saucepan, melt the margarine. Blend in flour. Add milk all at once and cook and stir until thick and bubbly. Add cheese and stir until melted. Stir cheese mixture into undrained veggies. Return large pan to heat. Add ham; heat through and serve.