There are several types of constructed wetlands. The first system is the reedbed or subsurface flow system. This is a system where plants grow in soil or gravel. In a pond system, also called the surface-flow, plants float on the water.
If you are installing a backyard wetland, plan for a reedbed system. The reedbed systems could be on bathtubs filled with gravel, mulched with woodchips and have wetland plants such as bulrushes, and cattails among others. The grey water in this system does not rise above the surface of the mulch, and people and animals do not come into contact with the grey water.
For a pond system, the greywater must be filtered by a reedbed first so that it reaches the pond without any odor or unsightly substances that may be unhealthy for animals and plants. Pond systems are not allowed in many state codes.
Bathtub and stock tank wetlands that originate from the washing machine systems and bathtubs, a surge tank, is installed and fitted with a one-inch outlet to allow the water flow slowly into the wetland. For larger wetlands an infiltration zone that is filled with two to four-inch cobble replaces the surge tank. A wood chip bio filter is important in reducing the flow rate of the water and removing the food particles.