What if we could use a drop of water twice? Once to wash our hands or take a shower, and then again to water some fruit or nut trees. Here’s how we designed our grey water system to do just that.
We live on an island that has limited fresh water supply, so when we were building our house last year we prioritized designing and building water systems for our homestead that are as regenerative as we could afford.
- We collect rainwater from our roof for our drinking water and household water.
- We chose composting toilets that use no water.
- And, we re-use the water that goes down our drains to quench the thirst of our orchards. This is called grey water!
I’ve had lots of people ask me how our grey water system works, so below are some details. Super importantly, we hired a wastewater engineer to design our system and professional installer to install it. We built a new home that needed to meet building code. In our area, working with professionals seems to be the way to achieve that. I am not one of those professionals so I don’t know all the proper technical terms, but I’ll do my best to be clear. Also, I wouldn’t consider this as a ‘how-to’, but my hope is that it piques your interest into what might be possible.
What is grey water?
Household waste water comes in 3 categories:
- Black water – water mixed with human feces, this usually comes from a toilet.
- Dark grey water – water mixed with food particles, like from your kitchen sink or dishwasher.
- Light grey water – water without food particles, like from your shower drain, bathroom sinks, and laundry.
Local regulations differ, but where we live, we’re allowed to use light grey water in our gardens. Black and dark grey water have to go to a septic field. At our house, we have no black water because we use a composting toilet.
Why choose grey water?
A grey water system allows us to use less water. Water we wash our hands with, we then re-use to irrigate plants instead of using drinking water to irrigate. For us, choosing a grey water system was additionally attractive because it allowed us to make use of our existing septic field. That field was too small to handle all of our household water (the new house we built was larger than the previous house that was here), but could work in partnership with a grey water system.
Choosing a grey water system also linked well with our composting toilets. The liquid waste (urine) from our toilets is separated from the solid waste. We compost the solid waste and the urine could either collect in a container inside the toilet (which we would then have to empty frequently) or be plumbed to connect into our greywater system. Since urine is high in nitrogen which growing plants need, this waste is really a resource!
Building a grey water system
Before installing our greywater system we shaped the land just downhill from our house into terraces. Our land is steeply sloped so these terraces will slow, sink, and spread water into the soil instead of letting the water roll down the hill and cause erosion.
The top terrace is next to the house on the downhill side. It’s a flat area for kid play and is seeded with a clover lawn and grass alternative mix. This is a very hot and sunny, south-facing area and our goal is to keep it green without watering it. So we have a shallow grey water seepage bed with distribution lines buried here. This is also where our 2 chamber grey water tank is buried.
All the other terraces as we move down the hill make up our growing food forest – a perennial food system that mimics natural forests. Picture fruit and nut trees, berry bushes, and flowers, herbs and vines all working together to increase diversity, habitat and food for us and for wildlife. Two of these terraces also receive grey water.
How grey water moves through our system
Light grey water leaves the house and goes into the tank. During the summer, a pump in the tank directs water to a shallow seepage bed and two mulch basins on terraces further down the hill. In the winter we direct the light grey water to the septic field by turning off the pump in the tank and letting the tank overflow into a dedicated pipe. This avoids water logging the terrace during our very rainy winters.
Dark grey water leaves the house in a separate pipe and goes down the hill to the septic field all year.
Constructing a seepage bed to water our lawn
The installation crew dug down about a foot and then added gravel. They laid perforated pvc pipes connected to the light grey water tank and then topped that with more gravel and landscape fabric. Finally they added some top soil into which we seeded clover and lawn alternative.
Constructing mulch basins to water our trees
At the downhill side of 2 of the terraces the installers dug a trench on contour, added gravel and laid the perforated pipe. Next they added these little green caps that help keep holes from getting clogged with debris. Finally they added more gravel on top, then landscape fabric and wood chips.
We did the finishing part of digging another trench, just downhill and parallel with the gravel filled trench with the pipe in it. It was about 1 ft deep and 1 ft wide and we filled it with wood chips. The idea is to plant trees just downhill of that wood chip-filled mulch basin.
That’s our system! It was completed in the fall of 2023 when we moved into the house. Over the winter we diverted all our grey water down to the septic system and we just really started using the light grey water to irrigate it in the late spring of this year, 2024. We’re still tweaking it, and hope to share how it’s working soon.
Resources
Would you consider adding a grey water system to your home? If so, here are some are resources to help you learn more.
Greywater Action is a group of educators who teach residents and tradespeople about affordable and simple household water systems that dramatically reduce water use and foster sustainable cultures of water. Their website is chock full of helpful resources.
Greywater Green Landscape is a great book by Laura Allen that has designs and do-it-yourself plans to conserve water and grow lush gardens!
If you’re in British Columbia, Canada, like we are, the Province published a Manual of Composting Toilet and Greywater Practice with all the details of what is allowed here. It is a technical document, but filled with useful info.
