Life... From Laundry! | DIY Grey Water Filter

In dry climates, keeping plants alive can mean using a lot of water — unless you reuse the water you already have. At our home, these plants are irrigated entirely with recycled laundry water, also known as grey water. The system is fully automatic and has been running reliably for over five years.

Grey water from sinks and washing machines is commonly and safely used used for irrigation, and in our case, it’s the only water these plants receive during the dry season. Without it, they wouldn’t survive. Instead of sending usable water down the drain, this system filters and redirects it to where it’s needed most.

In this Instructable, I’ll show how I built a simple, low-maintenance grey water filter using a 55-gallon food-grade plastic barrel, basic plumbing parts, and gravity. The washing machine’s existing discharge pump does all the work, and the filtered water feeds a rain barrel that supplies drip irrigation to the landscaping.

To make the filtering concept easier to understand, I also built a small, clear demonstration filter so you can see how gravel, pea gravel, and sand clean dirty water before scaling the idea up. That process is much easier to see in motion, so I’ve included a short video showing the demo filter and the full laundry grey water system in operation. You can watch it here before continuing with the step-by-step build, or skip ahead if you prefer still photos and written instructions.

These are commonly available materials, but for photos, sizes and options for any items you cannot find locally, I included links:

1. Barrel & Base
2. Food-grade plastic barrel with lid
3. cinder blocks
4. Filter Media
5. Gravel
6. Pea Gravel
7. Sand
8. PVC – 1/2 inch
9. 1/2" PVC pipe
10. 1/2"Elbow fittings
11. 1/2"Tee fittings
12. 1/2"Cross fittings
13. 1/2"caps
14. Straight reducer (NPT)
15. PVC – 3/4 inch
16. 3/4-inch PVC pipe
17. Elbow adapter (NPT)
18. PVC 3/4 Adapter, Sch40 Socket x NPT Male
19. 3/4" PVC Union Coupling Pipe Fitting, SCH40
20. 3/4 TEE PVC Fitting
21. 3/4" Elbow PVC Pipe Fitting
22. PVC Inline Check Valve
23. PVC 3/4" hose Barb x 3/4" Spigot
24. Misc
25. PVC Shower Drain
26. PVC spigot to female NPT reducer
27. 1-1/2 inch NPT cleanout plug
28. PVC cement

Tools

1. 3/4 NPT pipe nipple (Modified and used as a tap)
2. pipe wrench
3. cordless drill
4. hack saw
5. 29/32" hole saw
6. 3-1/4" hole saw
7. drill bits

Many, but not all, municipalities allow simple laundry grey water systems without permits. Check with your local building and safety department to find out what the requirements are where you live. You may have to file plans and get a permit before you proceed.

We're going to run pipes in an out of the top and also one pipe out the bottom along with a shower drain for flushing the system. For the pipes, my preferred method is with pipe threads, which requires drilling and tapping the barrel. For all three pipes, I use 3/4" NPT fittings to penetrate the barrel, so I drill the holes to 29/32", then form the threads with a modified steel pipe nipple. I just cut a groove through the threads on the pipe nipple to help them bite and clear the waste, then thread the nipple into each hole with a pipe wrench as shown.

To collect water at the bottom of the barrel to feed the outlet, I made this manifold of PVC pipe and fittings. The pipes have 1/4" holed drilled about 90 degrees apart with about 1-inch spacing along the length of the pipe. Precision is not required here, but the goal is for the holes to end up facing down. The attached pdf drawing shows the next part in detail: the final connection is made when the 3/4" NPT elbow fitting is threaded into the hole at the bottom of the barrel- from the outside. Once it's in place, I thread the female adapter onto the male thread from inside the barrel, then cement the manifold assembly onto it. I install the shower drain according to its instructions into the 3-1/4" hole in the bottom of the barrel, then cement in the bushing and plug.

It's important that the base is strong and stable, it needs to be built up on a firm, level foundation. If there's any doubt about settling, dig down and compact the soil below as needed to prevent shifting. I built my base up with the cinder blocks, glued together with construction adhesive.

Mount the barrel on the base and begin filling with gravel. A fully loaded barrel can weigh several hundred pounds, so make sure the base is stable before filling. Carefully fill up the space below the manifold first to prevent bending and breaking it. Then add the rest of the gravel on top. Next, add the pea gravel, then the sand. You want to leave at least 25% of the volume of the barrel empty at the top to hold water as it slowly flows through the filter. To prevent erosion of the sand due to water pouring it, I set a pie tin upside down on top of the sand as a deflector. I opened the plug under the shower drain an ran several gallons of water through to flush out loose dirt and sand. After flushing, I reinstalled the plug.

This is very much up to how you want to run your irrigation lines. As I said, I already had a rain barrel feeding my irrigation lines, so I ran the discharge of my filter into that barrel. You may prefer to connect your filter discharge directly to irrigation lines instead.

I ran PVC lines through the wall to the outside where they feed the barrel and return the overflow. At the top of the upper line, I add a TEE outside that connects the check valve I installed to prevent siphoning. I used my existing laundry discharge hose to connect the return line to the drain, then used my new longer hose to attach the laundry discharge to the upper line that feeds the barrel.

Run a laundry cycle to ensure the system flows as intended with no leaks. Once you are satisfied that everything is tight, you're in business! Your washer functions as normal, but now you're diverting water to your plants instead of just dumping it all down the drain. As long as you keep washing clothes, your plants are getting water!