Black water (or blackwater, sewage, toilet water) is heavily contaminated waste water that may contain human waste, pathogens, or other hazardous material. It needs to be safely stored until it can be disposed of appropriately. It is more contaminated than gray water.
Black water can be held two ways:
- A holding tank for later dumping at a dump station. This is more common in commercially-built motorhomes, travel trailers, etc., where pipes run directly from the toilet to an undermount tank.
- Inside a composting toilet, cassette toilet, bucket toilet, or similar. This is more common in self-built conversions. These must later be emptied at a dump station or into a conventional toilet, or securely bagged into an outside garbage bin (with permission).
Black water holding tanks generally need to have a treatment chemical added periodically to help reduce odors.
Due to its pathogenic content, it is NEVER safe or environmentally acceptable to empty black water onto the ground or into a storm sewer. It must always be emptied into a place designed to handle sewage.