BACK ACO Heavy metal filter ACO systems for rainwater treatment, including the metal roof filter, protects infiltration systems from pollution and congestion by deductible solids during the ingress of rainwater from, for example uncoated roof coverings from copper, zinc and lead. Water discharge requirements are very strict, because the water is classified as a heavily burdened. The metal roof runoff is purified by ion exchangers. The quality of water after filtration is so high that it can be introduced directly into the infiltration system (drainage trench or soak away), outfall, or into a rainwater using plant. It is also possible to use underground in seepage boxes or a soak away.