Grey Direct reuse of water is a common practice. Gray water from the bathroom can be used in gardening. Grey Water must be purified before use. With long-term use, salt, oil and grease and surfactants accumulate in the water. For direct use in gray water, the first application is to use the gray water coming out of the bathroom sink and washing machine directly in reservoirs without connecting to the waste water line. Secondly, it is used directly in garden irrigation systems. In gray water treatmentPhysical, chemical, or biological treatment can be used to reach the specified values.

In physical treatments; sand filter, coarse filter or membrane filter is used. In chemical treatment; electrocoagulation, photocatalytic oxidation, ion exchangers and granular activated carbon are applied. In biological treatment; artificial wetland (CW), RBC, SBR, MBR technologies are used. In order to ensure the standard in gray water recovery systems, filtration or sedimentation is done for pre-treatment, and UV or chlorine dosage is done for final treatment.