In a large saucepan, bring the broccoli, water and 1/4 teaspoon salt to a boil. Reduce heat; cover and simmer for 5-8 minutes or until broccoli is crisp-tender.
In a small saucepan, melt butter. Stir in flour until smooth. Gradually stir in milk. bring to a boil; cook and stir for 2 minutes or until thickened. Stir in the mustard, dill and remaining salt. Drain broccoli; drizzle with the mustard sauce.