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Everything You Need to Know to Build a Backyard Greywater Wetland
If you stop to think about it, it’s quite odd that we flush our wastewater into local rivers, isn’t it? It flows away, only to be siphoned off and cleaned by the community downstream before repeating the entire process once again. It would make more sense to use clean water for things like drinking and bathing and then use that same water again for things that don’t require a potable source, like irrigating the landscape. That’s exactly how many architects are starting to design houses and public buildings, but if you don’t live a housing development that features built-in greywater systems, you can make a few minor modifications to your plumbing system and create a greywater wetland that allows your wastewater to be recycled into the landscape.
First, it’s important to establish the definition of greywater: it is household wastewater that doesn’t contain any fecal matter, heavy grease or toxic chemicals. What goes down your toilet is considered blackwater, which can also be recycled, though it’s a bit more involved and is outside the scope of this article. If you put a lot of grease down your kitchen sink, that’s considered blackwater, too, as is any drain that you dump non-biodegradable chemicals in — if, for example, you’re a woodworker and you have a utility sink where you clean brushes with varnish on them, or the like. The shower and bathroom sink are usually fair game for a greywater system, along with the washing machine, as long as it’s not being used for washing dirty diapers. For vegetarians, the kitchen sink and dishwasher water can be used.
How to Build Your Own System
Treating greywater is really very easy. The hardest part will be configuring your plumbing to pipe it to where you want to use it and make sure it is segregated from any blackwater (the two are typically combined at some point under your house). For this part we recommend a professional plumber, unless you are the super-handy type. Once you get the greywater in a pipe that leads out from under your house and into the landscape, it needs to stay in the pipe until it passes through a small wastewater wetland that filters out soap and other gunk that’s in it. The greywater will flow by gravity, so the wetland must be built downhill from the house.
You will need:
Plastic kiddie pool
- Carpenter’s level
- 5-gallon bucket
- Rocks/gravel/pebbles (assorted sizes)
- PVC pipe and fittings
- Wetland plants, such as reeds, rushes, and sedges such as bulrush, cattail, horsetail, juncus, carex, etc.
- Set the kiddie pool on the ground and use a garden hose to trace the shape. A 4-person household should use an 8-foot diameter pool to provide adequate filtration for daily greywater production.
- Dig a hole equivalent to the size and shape of the pool. The goal is for the pool to sit completely flat (use a level) with the rim flush with the surface of the surrounding soil.
- Using a hacksaw, cut a 2-inch by 2-inch notch out of the side of the pool where you would like the water to flow out (this should be oriented downhill as it will serve as the overflow).
- Cut the bottom off of a 5-gallon bucket with the hacksaw. Then cut a 2-inch by 2-inch notch into the side of the bucket at the point where you just cut off the bottom. The pipe that brings the greywater to the wetland will enter through this notch.
- Cut another three or four 3-inch by 3-inch notches out of the top rim of the bucket and set the bucket in the pool with the rim side down on the opposite side from where the notch was cut into the pool. These holes will allow the greywater that spills in from the top of the bucket to flow freely out the bottom.
- Inside the pool, spread equal layers of cobblestones (3 to 4 inches in diameter), coarse gravel (2 to 3 inches in diameter), fine gravel (1 to 2 inches in diameter), pebbles ½ to 1 inch in diameter and coarse grit (about ¼-inch in diameter). The finest material will be on top with progressively larger rocks below. The bucket will be completely surrounded by the stones with just the top few inches sticking up, but should not end up with any stones inside of it.
- Position the outlet of the greywater pipe in the upper notch of the 5 gallon bucket and place a piece of flagstone over the top of the bucket as a lid.
- Plant wetland species directly into the pebbles on the surface of the pool, spacing them approximately 1 foot apart.
- Dig a trench about 8 inches deep and wide and about 20 feet long and fill it with wood chips to soak up the overflow water. These will slowly decompose and can be harvested as a soil amendment on an annual basis and replaced.
- If desired, use flagstone around the edge of the pool to conceal the plastic rim.
The wetland is now ready to receive greywater. After a day or two of use the water will begin to overflow from the notch that was cut into the rim of the pool. One option is to place another pool below the notch that is left free of gravel and used as a water feature. The advantage of installing a second pool is that it will serve as a holding area to use the water for irrigation purposes. This will still require a mulch-filled trench to overflow into on the downhill side, however.
As a final note, you should check with your local building department for rules concerning the use of greywater. Regulations vary, and it is still a ‘grey’ area in many places in terms of the code requirements. However, as long as you don’t bring the water to the surface where people can see and touch it, you generally will not have a problem with local authorities. Now that society is coming to terms with the fact that the human population is continuing to expand exponentially while supplies of clean freshwater are diminishing, solutions like this aren’t just a good idea, they’re absolutely vital for the health and well-being of the planet.
Images via Shutterstock
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