Grey Water System

Composting Toilet

For the longest time, I wanted to put a composting toilet in the Mill Creek NetZero Home (MCNZH). My reasoning is that, at some point, I think we're going to be forced to compost our waste for food production (*reader rolls eyes at raving hippie communist blogger*). Seriously, once the fossil fuel-based fertilizer is gone, how else will we keep our land fertile? 

Joseph Jenkins' book "The Humanure Handbook: A Guide to Composting Human Manure" is a must-read for people interested in long-term solutions to poo and pee. Composting them uses zero water and turns them into valuable products.

Once we started looking harder at composting toilets, though, we backed off. The reasons:

  1. A composting toilet such at the Pheonix system needs to be vented continuously to the outside. The 5 Watt fan would consume about 44 kWh of electricity annually. More importantly, though, it would mechanically expel warm air 24/7 from our house during heating season. So our super airtight home would become leakier because of this toilet. 
  2. These toilets are prone to outbreaks of flies. No kidding. Now, I'm pretty earthy - a regular Green Frickin Giant of earthitude. But I draw the line at having flies crawling out of my toilet bowl.
  3. The system would cost about $10,000 (if memory serves). That's a lot of money for air-leaking flies.

BRAC (Grey Water)

So, we went with the next best thing - in the MCNZH, we're going to flush our toilets with shower water.

Brac Systems is a Montreal-based company that sells tanks that collect washing machine and shower water (see picture above). In a new home like the MCNZH, you plumb the showers to drain into a big (300-450 litres) tank (there's an overflow that drains into the regular sewer system for when the tank gets full). Then, you run cold water pipes from the tank to the toilets in the home. 

The advantages of this system are:

  1. During the heating season, the heat in the shower water won't just escape into the city's sewer system. Instead, it will sit in the BRAC tank and be released into the home. That's a lot of heat (I'll add the calculation later when I find my formula).
  2. The 20%-30% of household water that go down the toilets will be "free" - we won't be flushing with potable water, but with water that was previously considered a waste product.
  3. We won't be pulling in 6 degree Celcius water from the city during heating season. At 40-60 litres of water per day, with such an energy efficient house, the amount of cold water that we won't need to heat up is significant (again, I'll publish the exact saving later).

I'm really excited to stop wasting so much precious drinking water on the toilet. In the climate-changed, water-constrained future, we'll all need to start being wiser with our water.

We'll be purchasing our BRAC system from Trimline Design Centre (on 6772 - 99th street ). Oh yeah, the systems aren't yet legal in Alberta. A minor detail - we're looking at the big picture here! It's only a matter of time before they become legal. Regardless, we're putting one in.

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Earlier this summer I was at the Boreal Center for Bird Conservation, up near Lesser Slave Lake. They have a very nice new all-eco visitor center, with composting toilets indoors, off the main lobby. They did work, in that they didn't smell, but I did have to wonder what the fans did to the winter heating requirements.

Yeah, they're becoming more and more common for rural applications. They especially seem to make sense in locations that water needs to be shipped to.

The only negative I have heard about grey-water recycling systems is that the toilet water becomes cloudy (but in the City of Toronto the average home would save about $200 per year using such a system) and that filter on the Brac system has to be changed a lot more often than they claim - at least once a week (and especially if you have the washing machine drain connected to it)

The filter concerns me a bit. I'm assuming that the cloudiness of the water will make the toilet bowls need cleaning more ofter, but that's not the end of the world.

Envirolet sells complete composting toilet systems for about $2000. They include all plumbing parts, compost bin, DYI instructions AND the solar panel to power the system. They've been used in remote areas up north and work great. No flies, no smell, minimal power usage and maintenance. Something to check out.

Positive ventilation, with some sort of heat recovery, is worth implementing on any energy efficient/indoor-air-quality-aware building.

Connecting the composting toilets to this ventilation
system would address the "blowing hot air out into the frigid wastes" concern, yes?

I propose to any conscious builder that taking a closer
look at ventilation in general is important.
What passes for ventilation in current state-of-the-industry is plain shitty... usually consisting of obnoxiously loud bathroom fans, drawing the smelly bacteria laden mist up through the nose-zone, and equally loud range hood fans which often blow the "smoke" back into the kitchen through either pathetically ineffective or expensive filters.

Even for the regular porcelain thrones, it makes a lot more sense to me to draw the bathroom air out either through or from down near the toilet to a central (quiet) fan - ditto for the kitchen. Proper design can minimize the ductwork.


Thanks for the comment, kk. The home will have a heat-recovery ventilator (HRV), but we cannot attach it to the composter's venting outlet due to cross-contamination concerns.

As for the bathroom ventilation, we will have no direct vents outside. Instead, there is a timer in the bathroom that puts the whole house ventilation on high gear for 5-20 minutes. That way, all ventilation goes through the HRV to minimize heat loss.

kk - That "smelly bacteria laden mist" is warm air that rises to the ceiling. That is why the fan is up there. You would need a good strong air flow to suck it out before it rises.

If you have a grey water system, would a drain water heat recovery unit be worthwhile? I assume the grey water system would capture the remaining 60% of heat that the DWHR did not get from a shower, etc?
What about just having the drain side of the grey water system in to a tank in the basement and let the warm water sit there to overflow in to the black drain? then you get the heat back and no pumps/flow lines required. Could even run the toilet lines through some heat exchanger located in the tank to preheat the incoming water?

It depends what you mean by "worthwhile" :)

The drain water heat recovery captures heat that is useful all year (even in summer). Having said that, the summertime is when we have the most solar heat available. So you have a good point. Perhaps a grey water system only, with the heated water heating up the space as it sits in the grey water tank, would have made more economic sense.

In the end we ended up scraping pretty hard against diminishing returns. Speaking of those, your toilet lines idea sounds like it would have pretty minimal payback.


Thanks for the response. I assume such a system would get around the fact that true grey water systems are still not allowed in the city (I believe this is still the case). Plus no pumps or filters to worry about. Come to think of it, the only time one might want cold water below 20C is when drinking it. If that's the case, you could just run the incoming city water line through this grey water holding tank to pre heat and chill drinking water as necessary or use ice cubes.

I've also wondered if shrouding a DWHR unit with a pipe and filling it with heat transfer liquid would help improve the efficiency. Maybe not by much since it already has conduction contact between the fresh water and drain lines (I assume metal to metal). Another option would be to replace other parts of the drain lines with sections of finned pipes to recapture the rest of the heat heading out the drain.

We put in envirolet composting toilets which has been very disappointing. My husband and I built our house and have lived here since July 2010. One pump burnt out due to a toilet that wasn't properly sealed. I empty 2-3 five gallon pails of pee-water and 2-3 five gallon pails of poop every 2 weeks (in an outdoor composting site-we live in the country.) The electronic flushing switch that flushed the toilet makes the poop water spray upon the lid and seat of the toilet. The aerator and rake bars are poorly designed and won't move. The heater also is poorly designed and dries only the small portion of peat moss-poop directly under the heater so the heater is not helping to evaporate the liquid. If you'd like a truthful assessment on this product (unlike their deceptive advertising) check out: or search Envirolet Poop Report

Ouch. That's too bad Laura.

some of those "composting" toilets seem to be configured more like "dehydrating" toilets...

the humanure system does not suffer from odour or fly issues, nor does it take any electricity or water...
problems are it is not very feasible in the city with a small lot and there are potential legal issues for composting human waste in certain municipalities.

it has been tested and proven for decades in several installations and would be great for an out-of-town solution.

Hi Conrad,

We have been thinking of installing a grey water system in our new build, and was wondering if the Brac System has lived up to the advertising? Any problems, complaints or better yet ways to improve the system?


Hi Jason,

We have purchased the unit, and plumbed the showers to drain to them, but we haven't yet installed the unit.

You see, it's currently illegal to install grey water in Alberta (illegal NOT to in some jurisdictions), and we haven't passed our final habitation inspection yet...


I was eagerly reading this post on your plans to use the BRAC system in AB, only to be dissapointed by your June statement of it being illegal in AB. Is this still the case? By the way, a big fan of the humanure book. Bought it when it first came out.

Can my house grey water back up and go
Into my septic tank? We do have alot of ground
Water so could our septic tank have a leak
Around the top? It was put in in 2002

Hi Conrad, I know the Reclaimed Water Working Group is planning to have some specs around the grey water systems soon. Do you know if they are considering the unit you have purchased?
Warm thanks,


Actually, I don't know anything about the Reclaimed Water Working Group. Can you provide any more details?


Hi Conrad,
How did you final habitation inspection go? Were there any significant issues with the grey water system?


We failed it because we have an illegal ship's ladder going up to our loft. Putting it there was a careless decision.

As for the grey water system, it is still sitting downstairs uninstalled. They are currently illegal in Alberta, so a sharp inspector would probably have failed us on it.

We do plan to install it at some point, but we've lost some momentum on the project.


As far as I understand, grey water systems for toilets are not necessarily ILLEGAL in Alberta, you just can't get a permit to install one meaning a plumber won't do it for fear of compromising his license due to a failure of the system. I designed and built my own system in the 1980's and when we talked to the government of the day, they would not change things to the plumbing code to address the installation of a system. We were informed that they basically had no cares about a system being installed in an " existing premises ". We must remember that governments make a lot of money controlling / selling water so realistically why would they mess with a cash cow. By the way, as I see it,the BRAC system along with most others that I have looked at, have a limited amount of grey water available for flushing and will require topping up with potable water. My system cleans the water for storage in a separate tank. As mentioned before, the water delivered to the toilet will be grey and murky requiring extra cleaning of the tank and bowl[ which on it's own is not a necessarily bad thing]. My system, when maintained provides clear water to the toilets. I say clear because the water is not disinfected although that is easily done. I had wondered how often the filter would need cleaning as I had unsatisfactory results when I tried that option in my system. I hope to market my system soon and it has taken me a long time to put all the pieces in place to provide something that is basically unparallelled in the market today. Something that will require minimal maintenance, minimal expenditures on supplies and optimal performance for years. There has been lots of information about the dangers of reusing grey water to flush toilets in the house however apparently there has never been a documented case of anything happening that has resulted in someone being harmed. My first system was built in 1985 and I have been living with grey water ever since. It does require some prudence but in the end, it should be encouraged in the future and with the way the price of everything is elevating, there is definitely payback potential. Sorry if I rant but this has been in my brain for a long time.

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