In a large pot, bring the water and chicken stock to a boil. Add the roux and whisk to dissolve. Add the garlic, onion, celery, diced ham, tomatoes and their juice, and okra. Bring back to a boil, then reduce heat and simmer until okra is tender, about 30 minutes. Season to taste with salt, black pepper, and Tabasco. Add shrimp and cook until shrimp turn pink. Adjust seasonings. If too thick, add a little water or chicken stock. Serve in large bowls with rice and garnish with chopped parsley.