Ham and Potato Soup

3 1/2 cups peeled and diced potatoes
1/3 cup diced celery
1/3 cup finely chopped onion
3/4 cup diced cooked ham ( I usually make this with left over Ham)
3 1/4 cups water
2 tablespoons chicken bouillon granules
1/2 teaspoon salt, or to taste
1 teaspoon ground white or black pepper, or to taste
5 tablespoons butter
5 tablespoons all-purpose flour
2 cups milk
Directions

Combine the potatoes, celery, onion, ham and water in a stockpot. Bring to a boil, then cook over medium heat until potatoes are tender, about 10 to 15 minutes. Stir in the chicken bouillon, salt and pepper.
In a separate saucepan, melt butter over medium-low heat. Whisk in flour with a fork, and cook, stirring constantly until thick, about 1 minute. Slowly stir in milk as not to allow lumps to form until all of the milk has been added. Continue stirring over medium-low heat until thick, 4 to 5 minutes.
Stir the milk mixture into the stockpot, and cook soup until heated through.