In Amsterdam, a decentralised alternative has been developed for an improved separate sewer system. That alternative is not only cheaper; the cleaner effluent means that it is also better. In the project on Erasmusgracht, rainwater is discharged into a separate sedimentation reservoir in the canal, after which it passes through the helophyte filter. It is subsequently discharged into the canal. The pilot project shows that the effluent from the sedimentation reservoir alone is better than that of improved separate sewers. In the sedimentation section, suspended particles settle, with the heavy metals bound to them. The subsequent treatment in the helophyte filter further improves the quality of the effluent. The helophyte filter serves primarily to remove the organic nutrients nitrogen and phosphates from the water. The two oval helophyte filters seal the sedimentation reservoir off from Erasmusgracht. The helophyte filters are lined by rock-filled gabions. The helophyte filters are open to the public and a bench has been placed by them. A sign on the bank explains the purpose and workings of the system.