If the RO water of your house also flows into the drain, then now you can use it in many ways. Most of the people have RO. Discharge or outlet of effluent.
Now you can use RO waste water at many places.
If you wash your car daily, you can use this waste water from RO.
If you wash the bathroom daily or mop the house then you can use the waste water coming out of this RO.
Not only this, the wastewater coming out from RO can also be used to water the plants.
You can clean any dirty place with this dirty water. This water is also useful for washing the house and courtyard during rainy days.