Friday, January 9, 2015

Progress report on water systems

Here is a brief update on how the water systems I've installed are faring.

Hot water

I have written articles about my hot water systems here and here.

The system was finalised at the beginning of September 2014, and has worked flawlessly since. We have not boosted it through Spring/Summer -- in fact, I have shaded the collectors to stop it boiling. Some things I really like about it:
  • I now have shorter "runs" of pipe between the hot water system and where I use the water, which means less waste
  • Because water is effectively heated instantaneously within the hot water system tank (discussed in previous articles), it has no taste, and so can be used to make tea and cook with. There is also no concern with Legionnaires' disease.

Rain water

I have written about our rainwater systems here and here.
We have been exclusively using rainwater since the beginning of September. This includes watering the garden, washing clothes and people, toilet flushing. At the beginning of September, we had ~35 kL of stored water of which I estimate about 30 kL is usable (due to the position of the tanks relative to input/output feeds, etc) -- this was not something I previously considered. Because the system was not completed until December, we did not capture the Spring rain maximally, and Spring rains were very sparse this year. It has been a relatively cool and dry Spring.
We have been very frugal with water, and have captured our washing machine grey water, and grey water from the kitchen for use on the garden (we don't keep washing machine grey water if washing nappies). Until last weekend, I estimate that we had used about 23 kL or a bit under 200 L/day.
I (very roughly)  estimate that this water is used as follows:
  • 6 - 8 toilet flush/day: 50 - 70 L daily
  • 1 load of washing / day: 70 L daily
  • kitchen sink: 30 L daily
  • garden direct watering: 50 L daily
  • bath/showering: 30 L daily
Clearly, the big users are the toilet and the washing machine. 


The toilet is a total loss, because that water goes straight to waste. I want to replace one of our flushing toilets with a composting toilet. This will save a lot of water, and also give us more compost.

Washing machine

Most of the washing machine water we use in the garden, though in a sub-optimal way. This probably seems like a lot of washing, but we have two young children, one of whom is in the process of toilet training (ie. we still wash nappies, as well as soiled clothing)


I generally wash in the shower every 2 - 3 days, and sometimes use the bath after the kids. They have a bath every 2 - 3 days. My wife often showers at work.

Lessons learned

  • Some water is easy to save, and grey water represents an easy saving if it displaces fresh water on the garden.
  • Timer taps make it easy to waste water on the garden. Also, it is hard to measure how much water is being used. I set up a timer tap out the back on the vegetables and fruit trees (separate circuits). Given the amount of grey water we have, it is almost possible to water all our trees and vegetables with grey water only (note that there are hygiene implications of watering vegetables with grey water -- make sure you do your research if you plan on doing this). In future, I will consider watering more by hand and less by the drippers
  • I accidentally let about 5000 L out of the tank via the vegetable drippers. I wanted to give the vegetables a bit of water before a very hot dry day, but forgot to turn them off until the next day. In future, I will never leave a tap running without an auto-off or an alarm to remind me.

Likely outcome for the Summer of 2014/2015

We will probably run out of water this Summer. I think we have about 5000 L (accessible) remaining in the tanks, which will last only about 25 days. I doubt we will get significant rain in that period. (We have had about 15 mm of rain in the last 4 days, which is very unseasonal, and is factored into this estimate). We are in the fortunate position to be able to switch over to town water easily.

Plans and thoughts for Summer 2015/2016

  • I would like to have one toilet replaced with a composting toilet by next Summer
  • I might add some extra sheeting to the pergola which will increase the rain collection area (very important for catching every drop of Spring rain)
  • We now have all the tanks installed and connected, so will maximally collect the Spring rains in 2015
  • I will try to do more to keep "dirty" clothes separately in the laundry, and wash them irregularly, keeping them for dirty tasks. This can hopefully ease the washing load


Water is one of those things that requires a whole system to perform well. Any compromises in subsystems will compromise the whole system. We are getting closer to the ideal that I modelled here, at which point I think we will operate (almost) solely on rainwater. I am hopeful that next Summer, even if we don't have a composting toilet, we will go a lot closer. Even this year we might well have made it through summer, had I not accidentally released that water. 
I think this system shows that it is possible to be self-sufficient for water with a relatively small amount of storage, however it does not leave any margin for error. In a fully off-grid scenario, I would want double the storage, even if it was rarely/never used. Of course, in such a scenario space would be less of a premium than it is in an urban environment!

This article was written by Angus Wallace, and first appeared at


  1. Hi Angus,
    Very wise making the most used water lines the shortest. I got the plumbers to do that here with the hot water in the kitchen. They originally set it up so that the kitchen was one of the last places that got hot water. I run a controller to stop the system boiling although that only affects the solar and not the wet back on the woodfire. Boiling can be a problem in closed tanks because the pressure can build. The tank in the roof here is open vented because of that.
    200L/day is very frugal - We're about 150L/day but don't have the same washing requirements. Good stuff, well done.
    The toilet is an interesting one as we have low flush cisterns 3L/4.5L flush. I've read you can put a rock or brick to displace water in the heavier water usage systems?
    Glad to hear that you received some good rain. 63mm here over the past two weeks! Awesome summer weather. Cheers. Chris

  2. Hi Chris,

    We haven't done any mods to the bathrooms here. One of the toilets is original 70s glory, and I've put the brick into it (tho I'm wondering if I can fit a second brick without interfering with the mechanism! ;-) The other looks like an 80s dual-flush. We generally try to apply the "if it's yellow, let it mellow" principle but often fall short. It's as much the loss of nutrients that bugs me -- I go to lots of efforts to get mulch and compost, and we flush lots of good stuff away -- insanity!

    I'm doing a bit of reading about setting up a biogas system, and hope I can combine a composting toilet with a biogas supply for the kitchen stove. I have no idea if this is feasible ;-)

    I'm really happy with our hot water system, because it's open-vented at atmospheric pressure. It has no circulating pump or controller of any kind. It heats water fine without power (as long as there's sun! ;-) The other thing about pressurised tanks is they only boil at about 150 degrees Celcius (because of the pressure) -- no wonder a tempering valve is advised! It'd suck to turn on the tap and get steam.....

    I'm still working on the plumbing for our auxillary tank for the kitchen -- brazing copper is not something I've done before, but I didn't want to pay another plumber! I'll get there eventually...

    I agree -- if climate change brings summers like this regularly, I'll be amazed though...

    Cheers, Angus

  3. Hi Angus,
    I'd be interested to hear what you come up with the biogas digester as I have no experience at all with them. I use a worm farm here (A&A worm farm systems) and I can't recommend it highly enough. I scare visitors by daring them to look into it - as a hint it doesn't smell at all. The nutrients go towards feeding the local wildlife that - hopefully - appreciate it.
    Cheers, Chris

  4. Hmm, it sounds like it is technically possible to set up such a biogas system to run on a family's humanure, but the yield is very small and not worth it:
    I think I'll aim to build a better solar-cooker instead. ;-)


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