In a medium-sized pot, combine the water, vinegar, soy sauce, and Worcestershire sauce over medium heat. Stir to mix.
Add the brown sugar, mustard powder, turmeric, garlic powder, cumin, and black pepper to the pot. Stir continuously until the sugar dissolves and the ingredients are fully combined.
Allow the mixture to come to a gentle simmer. Let it cook for about 5 minutes, stirring occasionally to prevent burning.
Remove the sauce from the heat and let it cool. Once cooled, stir in the cilantro (if using).
Transfer the sauce to a glass jar or bottle and store in the refrigerator for up to 2 weeks.