In a large pot, heat the chicken or vegetable broth and water over medium heat. Add the diced onion, carrots, celery, minced garlic, soy sauce, ginger, salt, and pepper. Bring the mixture to a gentle simmer.
In a mixing bowl, combine the flour, baking powder, and salt for the dumplings. Make a well in the center and add the egg and water. Mix until a soft dough forms.
Transfer the dumpling dough onto a floured surface. Roll it out to about ½ inch thickness and cut into small squares or circles.
Once the broth is simmering, carefully drop the dumplings into the pot. Reduce the heat to low and cover the pot. Allow the dumplings to cook for about 15-20 minutes, or until they rise to the surface and are cooked through.
Taste the soup again for seasoning and adjust with additional salt and pepper if needed.
Serve the dumpling soup hot, garnished with fresh parsley if desired.