Grey Water Disposal

I am going to do a few posts on waste disposal in a tiny house. Waste disposal isn't something someone thinks about unless it's not working or they don't have it. and you would think that your water that you use in your sink or your shower is mostly fine right?

Wrong, This water is called grey water and will actually rot and grow bacteria if left contained and untreated very long, sometimes as quickly as 24 hours. If left untreated and applied directly to plants in high concentrations certain chemicals and organisms will kill plants. If sprayed to cover a large area the aerosol bacteria produced can make you sick. Also if it is drained too readily into the soil it can affect its water bearing properties and kill your plants that way too.

It seems like a big problem right? Well at least it's not as bad as blackwater, which I will cover in another post. There are a few ways that you can treat greywater so that it can safely be used directly in food bearing gardens. however several of them are expensive and are really meant for large scale processing such as ultrafiltration, reverse osmosis, and distillation. The only one that I have thought of a sustainable solution for is distillation. This is the process of boiling water and condensing the steam to capture the water. The best part about steam is that steam can generate pressure, pressure can turn a turbine, turbines can create electricity, and electricity can be stored to power your home! are you as excited as I am about this? Probably not I'm pretty stoked.

I chose a parabolic trough because it is easy to build and move, super effective, and you only have to adjust it with the changes in the seasons, not hourly like with a parabolic spot mirror or fresnel lens. Just set it east-west, angle it toward the sun, and add greywater.

Anyways, the system is simple, concentrate the sun onto a container tube holding the greywater with one end coming from the feeder tank and and the other leading to the cooling coils. The idea is to use gravity to control the level of the water and make sure none gets into the cooling coils, which shouldn't be a problem if you are building this correctly. Another benefit is that you don't have an on or off switch as soon as the sun hits the parabola it will start boiling the water in the pipe no need for you to forget to turn anything on or adjust anything for a few months. It will run until there is no more water in the tank or the sun goes down, whichever comes first.

basically you start with a tank, it shouldn't be large to discourage wastful water habits and save space, but large enough to take a shower. I like RV graywater tanks because they mount right to the bottom of the trailer, how nice is that? No space to take up. If they dont already have one, you want to install a 3/4" male thread to the tank so you can run a hose to your distiller or to a treatment center if you choose to empty your tank that way, it gives you options.

The next component is the most important one, the parabolic trough mirror. This probably takes up the most space because it cant really be folded for travel. Basically you want a parabolic U. The idea is to concentrate all the rays you can onto one bar, the smaller you can concentrate it the better. next you need to make this U reflective, you can use various methods from polished aluminum flashing [that you probably have left over from building your tiny house anyways, a plastic flexible mirror, reflective spray paint, cd's, hard drive platters, crushed mirrors [although I heard alot of people have bad luck with that one :D ]  anything reflective works, the more reflective, the better it works. If you want to polish your aluminum flashing just take a pad of the finest steel wool you can find and start rubbing in a circular pattern, keep rubbing until you can see your face. thats it, just lots of elbow grease. If you want to speed the process along you can use brasso or some other polishing agent and a buffer but where is the fun in that? Just make sure you don't scratch the surface you are polishing. attach it to your parabola with some tack nails or screws or even better, a bonding agent. Dents and ripples screw up a parabola and make it harder to boil water but its your choice.

After you get the parabola set up and the reflective material applied find the "point" if your reflection. Take a board and hold it over the parabola while it's pointed at the sun, move the board forwards or backwards until you find the point where the line is the most concentrated, if you built it right that line should be 1/2" to 1". Mark the height of the line and drill holes to insert your boiler pipe.

On the other end [outside the parabola by at least a foot to make sure you dont accidently overheat your solder joints you want to make a 90* elbow and put a section of straight pipe at least 1 foot HIGHER than the highest point on your greywater tank. This will make sure no undistilled water gets into the coiling coils and contaminates your result. So the higher the pipe is the better.

At the top of this pipe you want a U and attach it to your cooling coil. All a cooling coil is is 50 feet or so of flexible copper tubing, shaded from the heat, you can do shorter cooling coil if it is submerged in water. Water acts as a great cooling heat sink.

The end result is distilled water. Take a sample of your water once you get your system running and send it to a lab for testing, if they give you the all clear and rate it as potable, you can even drink the stuff! Or just use it for a shower, or whatever else you need water for.

NOTE: Distilled water tastes flat compared to tap water, this is because almost all of the minerals in tap water have been stripped in the distillation process.

ANOTHER NOTE: You can also use a similar setup to this to distill ethanol that you can run in many gasoline engines.

THIRD NOTE? : The size of your parabola would depend on your climate, greywater usage, and the amount of sun you get. the general rule is "bigger is better" but when you live in a tiny house you can only do so much right? I mean, where are you going to store it when you move? I don't use alot of water so my system can be quite small [maybe 3'x5'] but I have seen some systems that were 40 feet long and 10 feet wide, your usage will be somewhere between those extremes, as for the pipe, don't go smaller than your beam of light, so around 1" for the boiler, the coil can be any size over 1/4"

FOURTH NOTE! I accept no responsibility if you blow your self up doing this. check your system on a regular basis to make sure everything is working, steam can raise to an immense pressure of restricted, and 900* steam blowing up on you is not a good day. so yea, be careful.


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  2. do you have any pictures of your system?

  3. I have a graywater system that drains directly into the ground. I have 3 values so I rotate where the water goes so it isn't to the same place every day. It take water from the Washing Machine and the kid's bath tub. I haven't had any problems with the ground absorbing the water or with it killing plants. I drain to some trees and bushes, to a grassy area, and in to the garden (no root plants). Your system seems overly complex if it is true graywater. As long as you don't use bleach or harsh chemicals, you don't need all that.

  4. It would be wonderful if you drew up some plans for your system, and included links for every part as if someone would just buy them all and put them together... most people would probably want to build their own, but at least then any part they didn't feel comfortable dinking around with, they would be able to just purchase;)

    I would love to be able to design a house around the idea of completely reusing all of the grey water (and perhaps having a composting toilet for the black water issue). Ultimately it would be wonderful to have a house that completely recycles all of its water, and simply adds water to the system as needed. Why do we send all of our water away to be treated when we could just distill it at home and keep reusing it?

    Also, I would like to know how often you need to clean out the distilling area? As you are boiling off the water, there would be precipitate left behind that would gunk up your system.... how often do you clean it out? Thanks.

  5. Hi! What about greywater in the wintertime? If the greywater tank is attached to the underside of the trailer, won't it just freeze :(?


    1. You should definitely have the space under your trailer sealed and insulated or it will sink the heat out of the trailer just as quickly as you can put it in. The tires should be off the ground anyways to keep the rubber from rotting. I recommend jacking it up and putting it on cinder-blocks that go around the parameter of the house.

      If you don't want to do the whole thing in blocks (they are heavy and way not portable) You can get attic insulation rigid foam board (extruded polyurethane with a layer of foil on it) and some foam insulation spray (great stuff), dig out a trench around the underside of your trailer and place the foam board between the ground and the trailer, using the spray foam as an adhesive and sealant)

      Once you insulate it you can keep a little 1500w electrical heater under there to keep the air underneath above freezing. If you read about the rocket mass heater you could build the mass under the trailer, and have a port where the chimney can rise through the interior of the house so it can convect and give you quick warmth while the bench would give you warmth in the long run.

      You should definitely protect under your trailer from freezing. Grey water or not, trailer life sucks in the winter if the bottom isn't insulated. (first hand experience!)

      Did that help at all?