PROCEDURE TO PURIFY THE LEACHED ONE.

A method and a device for cleaning leachate, the leachate after a collecting stage being conducted to several treatment stage, whereupon the leachate is led to a wetland system. This system comprises a sorption and a retention stage. During the sorption stage the leachate is taken to at least one dam (10) composed of two portions, one portion (12) consisting of a plant bed and/or a sorption bed, through which the water passes to another portion. The water is after the passage through the plant and sorption bed transported from the first portion (12) to the retention stage in the other portion (18) consisting of an open basin with a controlled water level.