Greywater and Blackwater - Introduction

Greywater describes wastewater that has been collected from a ship's galley, showers, laundries and sinks.

Blackwater describes wastewater containing fecal matter and urine. 

Greywater and blackwater are contained on ships in separate holding tanks.  On large vessels, whether or not the effluent is treated will depend on the ship's location and destination.  International rules for discharging waste varies from country- to-country.

• Best case scenario, the discharge streams are treated onboard by various means (screens, reverse osmosis or micro-biological processes) and then discharged into local sewers, or incinerated and bagged for shore disposal at a landfill.
• Worst case scenario the effluent is held and then discharged raw and untreated into the ocean. 

In either case the mechanical transferring systems that deal with these waste streams must be treated with caution as they contain all manner of bacteria.