Grey water, the gently used water from showers, sinks, and laundry, presents a unique opportunity for recycling. Unlike black water (toilet waste), grey water contains fewer contaminants, making it a prime candidate for treatment and reuse.

Mars Water Treatment Company manages the design, procurement, and installation of grey water treatment systems. Grey water is commonly understood to be wastewater from showers, bathtubs, and washbasins that can be recycled on-site for landscape irrigation, built wetlands, and toilet flushing. Because of the high levels of pollutants and nutrients, greywater frequently excludes discharge from kitchen sinks, dishwashers, and laundry machines. Although this type of recycled greywater is never safe to drink, it can be used to provide water for washing or flushing toilets in accordance with Qatari and WHO standards after going through a number of filtration and microbial digestion stages.