Constructed wetland cells are a newer system that allows some unusable lots to be used. The wetland cell is primarily a lined box with plants and overflow lateral fields that consume the rest of the effluent. The system generally consists of a primary tank with a large filter, control box (maintain water level), wetland box and the overflow lateral field. The effluent leaves the home to the septic tank for pre-treatment. The filter keeps most of the solids in the tank, the effluent moves to the wetland cell where plants and evaporation remove most of the bacteria and effluent. If the box does have excess effluent it moves to the control box and then the overflow lateral field where the rest of the effluent is treated.