Sunday, September 30, 2012

Grey water system in cold climate

We’ve been kind of shy to discuss some of our thoughts and ideas about typical building practices. One of those parts is plumbing. It’s kind of a stinky subject as it is. I’ll leave the most noxious part of that subject to another post. This post is supposed to illicit comments and discussion regarding grey water (not sure if its grey or gray, both work) usage and deployment particularly in a cold climate.

It is a fairly common practice in warmer areas of the world to use waste water as a means to irrigate plants and shrubs. We bought some of the material found at the Oasis Design website and have used the material as a guide as we’ve designed our grey water system. In all these materials there is about 3 pages discussing the theoretical possibility of using the system in a cold climate (Milly has highlighted them all and refers to them often.) I’ve read other material such as Graywater gardening, an Australian company that focuses on water reuse, but our main purpose this first year is to get rid of water. We are not concerned at this point with water efficiencies.

With the almost 100% of imminent disaster predicted by our professional plumber we have committed 100% to this concept.

With a bunch of theoretical knowledge we’ve dug right in and have installed a very simple grey water system that will get rid of water in one location. We have much more planned where we will actually put to use the waste water but the winter is coming and we need to get something in place before we are knee deep in you know what.

Here’s what we’ve done so far.

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The distribution plumbing exits the house on the south. Our hope is this will be the warmest location to help with freezing. We are making an insulated box along with filling in dirt and straw to keep the exit point above freezing.

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We have dug a small trench that slopes down hill to the side our our place. The run is about 80 feet from the house.

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I dug it by hand but I hear you can rent a small trencher that makes this process easier. I’ll probably do that with the other branches we have planned next year.

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You can see another pipe heading to the right of the picture above. The connection value is a three way value. If the pipes do freeze I’m hoping to use the alternate pipe as backup in case I need it.

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We took a clear hose and used it as a water level to figure out elevation. Kind of a cool thing. I didn’t have any ideas how they worked before doing this project. We then tied a string to use as a guide and used a 4 foot level every 4 feet to make sure the pipes continually sloped down hill on at least a two percent grade.

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At the end of the pipe we’ve dug out a roughly 8’x10’ mulch basin. We did percolation tests and our soil absorbed water pretty decently and this is how big we calculated for our needs. This mulch basin will be dug out just a bit more than wood chips, grass clippings, etc. will be the cover for winter time.

Everyone tells us this will freeze over in no time. Well everyone except the people we’ve talked to that have put in a grey water system themselves. I’m more inclined to be hopeful rather than pessimistic but it’s hard not to question our sanity when we think of –40 Celsius.

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We planted a tree at the end of the basin in the hopes of it using lots of water in the future. We hope it survives as it was out of water for a few days and the leaves were crunchy when we planted.

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It’s been getting a daily dose of water for the past week in the hopes of helping it survive.

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We covered the pipe after it was carefully set out and sloped correctly.

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There is about a 10 inch fall from the pip to the bottom of the mulch basin. The theory is the water will drain after each use thus the pipe doesn’t get frozen solid as you would expect. It is also warm water coming out so that helps keep the pipe from freezing up. The drop allows the water to not sit at the end of the pipe where it can freeze more.

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We are going to cover the pipe with a good layer of straw and other mulch clippings. We hear you can do this over carrots all winter so figure this will work for a pipe that has warm water flowing through it.

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All covered up. We will still add insulation of some sort over the ground. We are thinking loose straw

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I have two other sissy pipes as alternatives in my main pipe freeze up. I call them sissy pipes as I’m not at all confident with this experiment with grey water. I’m being a wimp and having a couple more options that hopefully will see me through until the main pipe can be unfroze.

I’ve also had my pessimistic plumber route a hot water option for my outdoor pipe just in case I need to shoot hot water down the pipe to unfreeze the mainline.

As a little project this year with this we are also going to take daily temperature readings on the mulch basin soil and record the outdoor temperature as well.

If you have any suggestions or comments please let me know or at least wish us luck.


  1. 'Over-designing' Engineer ;-)October 2, 2012 at 10:15 AM

    You do know what the "big-bad" & "overly conservative" engineering community has to say about this 'experiment'; so I won't bother repeating myself...That said, GOOD LUCK!
    What diameter pipe did you install? How deep did you bury the pipe? Did you add any cleanouts to give you access to the pipe? How deep did you go with the 8x10 mulch pit?
    Congratulations on the discovery and use of the water level...I believe the Romans developed that...we still use levels (optical or laser, now) in construction.

  2. We went 2" inside house then switched to 1.5" outside. We have a 3 way diverter value that acts as a clean out.
    We buried the pipe about 3 inches but will cover with mulch and insulating type materials for about a foot or so above. The mulch pit is going to end up about a foot deep but will be covered above that as well.

    We are hoping the composting nature of the mulch basin will keep the pit naturally warm as well.

    I'm sure thankful for those Romans. We didn't know anyone with a transit level.

    Any other thoughts, comments, or warnings by the over-designing engineer folk out there? I'm mostly looking for advice or suggestions as we are truly experimenting with this.

  3. Very interesting post. We've been researching this as well and found the same resources. Of course, we live in one of those milder climates you mention. This sort of thing is well off the radar of most professional plumbers, so a pros prediction should be taken with a grain of salt. Having said that, I can't claim any design or engineering knowledge, we're in the same boat as you,!

    One thing we realized in our research, is that each system is unique to where it's installed, so I don't think it's necessarily a bad thing to jump right in. That's what we plan to do. Hopefully the glitches will be few!

  4. @Leigh- Well, if it works for us it should work for you. I'll keep you updated to our "should have done's". Right now freezing is a major concern and if you don't have that to worry about it would be a delight.

  5. It sounds like you've gone to a lot of trouble to get things right, I hope it works for you! We drain our bath and washing machine water into a drum under the house (house is raised up about 1m off the ground) and pump that water onto our vege garden each day. This is technically illegal in our state, but we'll just change it back before selling the house (hence the temporary nature of it), and can send all water to septic if we want to through a three-way valve. I know you're not using the water at first, but I just wanted to tell you that you can use it, we have been using it for 3 years, with no problems with plant or human health. If you can put your garden downhill from your house you won't even need a pump! In winter, if we have more water than the garden can use, I just put the sprinkler on the lawn instead. Cheers, Liz

    1. We've considered using a surge tank but decided to make it simple this go around as I think a surge tank may have issues in a really cold climate. I think we will use the grey water on our fruit trees. Still haven't decided on our garden. Glad to hear it worked for you as that gives me some encouragement.

  6. We had an arrangement much like what Farmer Liz describes for the washing machine water when I was a kid in WI. We called it a dry well, and the drum was buried in the back yard. I don't remember it ever having a problem, even in a WI winter.
    Thank you for the informative post. We'll by buying and making our own place in MT soon and can use all the info we can get!

    Minor copy editing: "illicit" means roughly "illegal". "Elicit" is the term you want in that spot. "Grey" is the common British spelling, "gray" is the common American spelling, both are correct, as you said.

    1. What part of MT? We moved from there after being in NW MT for about 5 years.

  7. Thanks for posting your experiment, Doug. I'm in the same situation, only I also have a high water table to complicate things. The good thing is that I'm on sandy soil. Since my foundation will be 32" above ground, my thoughts, at the moment, are to construct an above-ground mulch pit ringed with 2 layers of straw bales. I would cover it with a board and put straw bales on top of that for insulation. I currently use a sawdust toilet, but the compost pile freezes in the winter - it's too cold for microbial action, as someone suggested above. (At least the top freezes - I had ground squirrels burrowing in it last winter!) However, I'm thinking that if I make the mulch pit significantly bigger than the current compost pile, it might not freeze, especially with the addition of warm water. The trick will be to prevent the line from the house to the pit from freezing, if water only goes through at a trickle (e.g. when rinsing dishes). I wonder if I could somehow run the pipe lengthwise through hay bales...

  8. We have put straw over top of the line out to our mulch basin. I have covered the mulch basin with leaves and straw as well. I've considered covering with plywood that has been lined with blue board insulation but think snow might do the same. We also get chinook's here where snow melts and it warms up periodically during the winter. I'm hoping that if everything freezes over I'll be able to use my backup systems for a while until I can thaw everything in the main line. Our mulch basin is roughly 2 feet high (covered with staw) and 8x10 feet wide.

    I might get line the mulch basin on the north with bales but haven't done it yet.

    I'm hoping my compost pile doesn't freeze. It's been in place for a few months so hopefully it doesn't.

    I think I wouldn't run it through the bales and leave the pipe in the ground. At least that's what I'm doing.

  9. Can I ask how this has gone for you over the last year and a half?

    Very interested to know

  10. We have used the grey water system for two winters now and no matter what the temperature is outside (got to -48 c this winter) the grey water mulch basin is always between 50 and 60 F. It's amazing. We planted a tree around the pit and it has three to four times the growth of other trees we planted around our property. Huge success. We are going to expand and make several basins around the place in the future.

  11. What happens when the mulch decomposes?

  12. We clean out the mulch basin every year. Then add new mulch/covering.