The Rynfield WCW is situated south-west of the Van Ryn Dam in Benoni and falls within the DD5 area. Built in 1969 and extended in 1979, it is designed to treat 13 Mℓ/d of raw sewage from the Benoni, Cloverdene and Rynfield areas. Both biological filtration and activated sludge are employed as treatment processes.

A central inlet works, incorporating the processes of screening and grit removal serves the works. The older biological filtration module includes primary sedimentation, biological filtration and humus clarification. The BNR activated sludge module consist of a 5 stage reactor basin and final clarification. The final effluent is chlorinated before discharging it into a tributary of the Blesbokspruit.