In a large skillet over medium-high heat, cook the pork until it is no longer pink, about 5 minutes. Stir in the chili powder, soy sauce, sugar, and salt. Cook, stirring frequently, until the sugar is completely dissolved. Remove the pan from the heat and add the water. Bring the mixture to boil, then cover and simmer for 20 minutes, or until tender. Serve with sour cream, if desired.