Grey Water Toilet Helps Keep You Flush

The average first world household swims in an ocean of non-potable water from things like HVAC condensation, shower drains, and periods of rain. All of it just goes to waste. These same households pay the city to deliver drinkable water to places that don’t need it, like the toilet tanks. Isn’t it time to put all that perfectly good grey water to use? With a zero city water toilet, you can give that slightly-used H₂O one last hurrah before flushing it down the drain.

When the toilet is flushed, an ultrasonic sensor in the toilet tank monitors the change in water level and triggers a pump to fill the toilet back up from a barrel in the basement. A clear plastic tube inserted into the toilet tank does double duty as both the water source and tank overflow drain point.

The 55-gallon plastic barrel in the basement collects water from both a shallow well and condensation from [nodemcu12ecanada]’s gas furnace. A NodeMCU controls the 12V submersible pump to send water up to the toilet, and another ultrasonic sensor monitors the water level in the barrel.

This setup doesn’t require changes to any of the existing plumbing, and reverting back is easy. We particularly like the use of phone plugs and jacks as quick connectors, and will likely steal the idea. You can get more information about this and [nodemcu12ecanada]’s other home-automation projects here.

43 thoughts on “Grey Water Toilet Helps Keep You Flush

  1. In Europe, modern boiler condensate tends to be full of nitric and possibly sulphuric acid, to the point where it can discolour brick work. I’m not sure I’d want that in my toilet – it’d make cleaning with bleach very difficult.

  2. This setup doesn’t require changes to any of the existing plumbing, how? Acidic water from furnace and electronics in tank, a potential mess. A tank and gravity feed in the attic charged by rain would make more sense. The well in winter. This is not grey water just a well and no shower or laundry water is being reused. Since sewage rates are made from water use, you are cheating the sewage costs.

  3. The condensate waste from condensing gas furnaces is highly acidic, and is well known to corrode copper among other metals. I wonder if potential damage over time to metallic parts inside the toilet tank was taken into consideration?

    1. A lump of marble or concrete in the reservoir might buffer the acidity.

      Runoff from a shower or hand basin is likely to turn into black water if allowed to sit for any length of time, and contain hair and other pump annoying things… it’s usually best left to run directly into a garden bed.

      Rainwater is considered potable in many parts of the world, and its use for toilet flushing is even mandated in the building codes of more water scarce regions, to reduce demand on reticulated town water supplies.

  4. While I applaud the re-use of gray water, many urban septic systems need the “fresh water” for both getting the waste to the treatment plant and in the treatment process.

    Also, in my small community, your sewer bill is based on your water consumption. I could see bureaucrats going ballistic about unmetered water (rainbarrel, condensate) being added to “their” systems.

    1. That really depends on where you are. In my neck of the woods, there is so much groundwater that leaches into the sewer lines, that the treatment plant ends up with a comparatively dilute input.

  5. In my city they installed two seperate water pipe systems in new homes, about a year of 15 or 20 ago. One had very clean drinking water running through it, and the other one less clean drinking water to flush the toilet with, or irrigate the garden with.

    But with time passing by water requirements for the toilet water also increased, which made it more expensive. Also the two seperate systems were confusing. I think there even were pipes accidently swapped at some houses, which meant that perfectly clean water was used to flush the toilet, and the dirty water was used to drink and shower under, which eventually lead to people getting sick.

    It wasnt long before they shut it down entirely, as it just was an absolute fail. It was expensive, not really safe and deffinitely not environmently friendly requiring a seperate pipe system.

        1. Well actually, in large enough water and sewer pipes you have to have HUGE concrete blocks on the ‘end’ of turns, so that the water pressure (and changes in) don’t blast the turns off the end of the pipes….. so yes, water does care, but in a different way.

    1. I’m planning on doing this when I build my new house in a couple years. My site has a well, but is now on city water because the town polluted the groundwater with an improperly handled landfill and installed city water as a patch instead of fixing the problem….

      I plan on flushing the toilets and watering the grass with the well, and drinking the city stuff.

  6. The two systems/infrastructure that I hope we’ll see in our homes (soon/next): 1. Commercial grey water systems. (My ‘roll your own’ system would definitely wait until I had some sort of guest/s at the house to go out.) 2. Separate breaker box/power distribution for DC power. (With a common outlet fixture type for wall outlets as well.)

  7. I’m missing something here. Why can’t this barrel be filled with a simple float controlled automatic pump? Why all the smarts, unless the toilet is required to be an IoT device monitored over the net?

    Years ago my Dad dug out a basement darkroom under our house which was built on Sydney sandstone. Because the water would always seep slowly through behind the concrete-sealed rock, we had a drop in the corner that went down a metre or two below the darkroom floor. A hysteresis float controlled pump would run when the seep water got to a preset level then pump it dry in about a minute. It used to trigger every week or three in dry weather and every day or so in extended wet weather. It worked like a charm.

    1. There is no need for ultrasonic and electronic inside the tank. It’ll just add reliability issues due to water/corrosion.
      It is a matter of attaching a small magnet to the float valve arm and use of a potted reed switch to detect the magnet.

  8. If you think A/C condensate is clean, you’ve got some trouble coming. I can’t count the hours I’ve wasted because household systems don’t come with any instruction, and nobody knows about the bacterial detritus building up in their condensate drain or their condensate pump. Without any treatment that toilet tank is going to look like a biological experiment gone wrong in no time.
    Oh, and Legionella. Look it up.

      1. But is the added cleaning more or less ecologically friendly than just using clean water?
        Genuine question – it’s easy to neglect issues like added cleaning or reduced lifetimes of devices.

  9. So, it increases the amount of soap and other chemicals you must use to clean toilet bowl with the now dirty (understand full of bacteria and biofilm & other yellow minerals). In the end, I’m not sure it’s more ecologic. If you really want to do something better, use dry toilets or go outside (if you can).

  10. Needles to say, but check local regulations and rules.

    Then, of course, decide to do it or not regardless … but be informed.

    I believe in Australia only rain water can be used for flushing, instead of expensive drinking water.
    And all pipe work is to be done by a licensed plumber.

  11. Maybe they can the water through a simple filer to remove the soap if there is any? When I have a bath i think it’s crazy that I can’t use the water for anything else and it’s the soap that’s the issue so if there was a way to stop the soap being an issue that would be great.

      1. Soap is designed to break down oils and oil is a plant’s blood. I make a pretty potent weed killer that is just water, dish soap, and vinegar. No way I would purposely put water with soap in it on my plants. Also, classifying water from a dish washer as “grey water” is dangerous. The amount of bacteria and bacteria food in the output of a dishwasher makes it unsafe to store or use for most applications where “grey water” is acceptable.

  12. Would like to see a total cost benefit analysis
    The cost of all the parts (bits for free doesn’t count, original costs thanks)
    Time factor
    Cost of electricity to pump vs cost of city water
    Servicing / MTBF failure of pump costs

    What’s the payback? 300 years?

    Or in other words
    Beyond virtue signalling there doesn’t appear to be much point
    Chalk it up to the right reasons – because you can, not for any environmental benefit – then its a good project

    1. I was going to type a comment, but you and others have already said nearly what I was thinking.

      Just because the water ‘disappears’ and you don’t understand the system, doesn’t mean it “just goes to waste”. Maybe instead of making assumptions from a place of self prescribed moral superiority, the author of this article and the maker of this project should spend some time on education.

  13. In Japan it is common to see toilets that have a small sink on top of the toilet tank. When you flush, the tap on the sink starts to flow, and it flows through the drain hole in the sink directly into the toilet tank filling it up as usual, only now you can wash your hands in it. Saves water as well as space in the bathroom!

    1. If you check the details for those toilet tank sinks, you’ll find that the water from the sink portion doesn’t go into the toilet tank, it goes down the overflow tube which feeds it into the toilet bowl itself. The tank never has water from the sink in it. Each of the 3 models I looked at have the top fill tube feed the sink faucet, and the toilet tank itself is filled from the bottom valve of the tank water intake. In other words, the ‘bowl’ portion of the incoming water is diverted to the sink, which then feeds it directly back into the bowl — and not the tank itself. I thought this general concept seemed ok until I realize that you have to wash your hands with cold water, and I’m a fan of washing my hands with hot water after using the toilet, even if I don’t get my hands ‘dirty’. To me it’s just proper hygiene, and using cold water isn’t a great option IMO, nor is the casual ‘rinse’.

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