A cartridge for filtering water contaminated with hydrocarbons comprising at least: - a pre-filter comprising at least one conduit, configured to accommodate a first filtration material, - a filter comprising at least one conduit, configured to accommodate at least a second filtration material, and - a fixing system configured to keep the conduit of the filter and the conduit of the pre-filter assembled, the fixing system comprises at least one assembly ring, now assembled, in a removable manner relative to each other, the conduit of the filter and the conduit of the pre-filter, the cartridge comprises three removable parts: the filter, the pre-filter and the assembly ring, the conduits of the filter and the pre-filter are fixed juxtaposed to one another, the assembly ring has a first part configured to extend opposite a part of the conduit of the filter and a second part configured to extend opposite a part of the conduit of the pre-filter, the first part of the ring has a length Lba2 over which the first part covers and contacts the conduit of the filter, and the length Lba2 of the first part of the assembly ring is greater than a length Lba1 of the second part of the assembly ring, the cartridge being characterised in that: the length Lba2 of the first part of the assembly ring is at least twice greater than the length Lba1 of the second part of the assembly ring, the length Lba2 over which the first part covers and contacts the conduit of the filter and the thickness Eba2 of the first part of the ring over the length Lba2 are configured to withstand the pressure exerted at least by the contaminated water during its passage through this conduit. - a pre-filter comprising at least one conduit, configured to accommodate a first filtration material, - a filter comprising at least one conduit, configured to accommodate at least a second filtration material, and - a fixing system configured to keep the conduit of the filter and the conduit of the pre-filter assembled, the fixing system comprises at least one assembly ring, now assembled, in a removable manner relative to each other, the conduit of the filter and the conduit of the pre-filter, the cartridge comprises three removable parts: the filter, the pre-filter and the assembly ring, the conduits of the filter and the pre-filter are fixed juxtaposed to one another, the assembly ring has a first part configured to extend opposite a part of the conduit of the filter and a second part configured to extend opposite a part of the conduit of the pre-filter, the first part of the ring has a length Lba2 over which the first part covers and contacts the conduit of the filter, and the length Lba2 of the first part of the assembly ring is greater than a length Lba1 of the second part of the assembly ring, the cartridge being characterised in that: the length Lba2 of the first part of the assembly ring is at least twice greater than the length Lba1 of the second part of the assembly ring, the length Lba2 over which the first part covers and contacts the conduit of the filter and the thickness Eba2 of the first part of the ring over the length Lba2 are configured to withstand the pressure exerted at least by the contaminated water during its passage through this conduit. the fixing system comprises at least one assembly ring, now assembled, in a removable manner relative to each other, the conduit of the filter and the conduit of the pre-filter, the cartridge comprises three removable parts: the filter, the pre-filter and the assembly ring, the conduits of the filter and the pre-filter are fixed juxtaposed to one another, the assembly ring has a first part configured to extend opposite a part of the conduit of the filter and a second part configured to extend opposite a part of the conduit of the pre-filter, the first part of the ring has a length Lba2 over which the first part covers and contacts the conduit of the filter, and the length Lba2 of the first part of the assembly ring is greater than a length Lba1 of the second part of the assembly ring, the cartridge being characterised in that: the length Lba2 of the first part of the assembly ring is at least twice greater than the length Lba1 of the second part of the assembly ring, the length Lba2 over which the first part covers and contacts the conduit of the filter and the thickness Eba2 of the first part of the ring over the length Lba2 are configured to withstand the pressure exerted at least by the contaminated water during its passage through this conduit. the length Lba2 of the first part of the assembly ring is at least twice greater than the length Lba1 of the second part of the assembly ring, the length Lba2 over which the first part covers and contacts the conduit of the filter and the thickness Eba2 of the first part of the ring over the length Lba2 are configured to withstand the pressure exerted at least by the contaminated water during its passage through this conduit.