Remove strings from beans. Cut beans into 1 1/2-inch pieces, and wash.
Place water and ham hock in a large Dutch oven; bring to a boil. Reduce heat; cover and simmer 1 hour. Add beans, sugar, salt, and pepper; cook 50 minutes or until beans are tender. Remove from heat; drain and add butter. Cover and let stand 5 minutes or until butter is melted. Toss beans well before serving.