Melt butter in a large Dutch oven over medium-low; whisk in flour. Cook, whisking constantly, until mixture turns golden brown, 10 to 12minutes. Increase heat to medium, and add onion, celery, and garlic. Cook, stirring often, until soft and golden, about 15 minutes.
Stir in bell peppers, and cook, stirring often, 5 minutes.Stir in broth and water, and cook, stirring constantly, until mixture thickens,7 to 10 minutes. Stir in shrimp, and cook, stirring occasionally, until shrimp turn pink, about 5 minutes. Stir in hot sauce, salt, and pepper; cook 5 more minutes. Stir in scallions and parsley, and simmer 5 minutes. Remove from heat.Cover and let stand 5 minutes. Serve immediately over hot cooked rice.