Black water can indicate growth of sulfur-reducing bacteria inside a hot water tank set to too low a temperature. This usually has a strong sulfur or rotten egg (H2S) odor and is easily corrected by draining the water heater and increasing the temperature to 49 °C (120 °F) or higher. The odor will always be in the hot water pipes if sulfate reducing bacteria are the cause and never in the cold water plumbing.[citation needed] Learning the water impurity indication color spectrum can make identifying and solving cosmetic, bacteriological and chemical problems easier.