The discharge from water closet and urinal is called Black water.

• Refers to waste water discharged from water closets and urinals. It contains human excreta. The black water is discharged into public sewerage system or a septic tank.
• The black water in the septic tank is broken down by bacteria in the septic tank and is partially digested. This black water which undergoes treatment in septic tank is called Septage.
• Grey water does not include the wastewater from toilets, urinals or bidets. The discharges from these fixtures are classified and sometimes referred as black water, because they contain high levels of pathogenic organisms and solids. Such discharges should undergo specialized treatment prior to any secondary use.