A few words about composting toilets

I’ve been meaning to do this post for a while, and since we aren’t doing much around the trailer right now, I thought this would be a good time to cover this topic.

Composting toilets are very often lauded as a more environmentally friendly option for dealing with human waste and this is the subject that I would like to address here.

There are many different kinds of composting toilets, from the home made to expensive contraptions. Kat and I decided to go with the non-electric version of the SunMar Excel, pictured below.


We didn’t know much about composting toilets when we bought it, but now that we have been using it for about eighteen months or so, we have a pretty good idea of how it works. We also have had to deal with some issues.

Our toilet has a simple drum chamber where the solids collect. There is a screen that allows the liquids to drain into a dehydration tray. You add bulking material and spin the drum using a crank handle to mix up the contents. Fairly simple stuff. After a while, you move some of the material from the drum into the “aging tray” at the bottom and let it sit undisturbed for about six weeks and then, according to the manual, it should be ready for use as compost.

But is this system more environmentally friendly than using a conventional water-based toilet? Let’s look at the details.

First, construction. Most conventional toilets are glazed porcelain. When they break, there really isn’t any way to fix them, so they usually end up as waste at the landfill. This is not a good thing. There have been some articles I have read that say the porcelain can be crushed and used as aggregate for concrete, but I don’t know how often that actually happens.

What about our SunMar composting toilet? Well, it’s primarily made of plastic. There aren’t any recycling symbols stamped on it, so when the toilet breaks beyond repair, it too will end up in a landfill. Both the porcelain and the plastic will last seemingly forever, in terms of breaking down. No one really wants a compostable composting toilet.

Okay, so you aren’t really gaining anything with the construction, at least with these commercial versions. How about daily usage?

Water, of course is always the biggie. Conventional toilets use water as their transport mechanism. Most toilets today are low-flush, meaning the amount of water they use is less than in the old days, but you’re still using fresh water (in a conventional home) to flush your crap away. Depending on the size of your family, this can account for a large majority of the water being used.

With the composting toilet, you don’t use any water at all. However, you do use bulking material. Our SunMar toilet came with a bag of this stuff and you can buy more bags from the store. Their recommended bulking material is 40% peat moss, 60% wood shavings. A bag of this stuff runs $20 and it will last roughly 2 weeks for two people. That’s in addition to buying toilet paper, so now you have additional charges for using your composting toilet. On top of that, peat moss is a controversial material as far as the environment goes as it has been debated just how well it can recover after being harvested.

What we ended up doing is ditching the store bought bags of bulking material and just using wood shavings, which I can generate in large quantities using our planer. We also stopped using that aging tray mentioned above. Once we did that, we eliminated the gnat problem we were having during the summer. Which is another issue you generally don’t have to deal with when using a conventional toilet: insect infestations.

So, the purchased variety of composting toilets can end up costing you more per daily use, if you strictly follow the recommendations from the manufacturer. On the other hand, if your house is connected to a municipal water grid, you will likely have a water bill as well which your conventional toilet would be a prime component of, so it may equalize out in the long run.

How about electricity? Our toilet is a non-electric version so we don’t use any electricity at all. Your conventional toilet will use some electricity to run the pump to refill the tank. There are also compositing toilets that use electricity to run fans and a heater to speed up the composting. With those, expect to use way more electricity than your conventional toilet as using electricity to generate heat is not very efficient.

Now there are simple, homemade composting toilets. These might be a simple outhouse style or even just a bucket-loo. The bucket toilet is about as simple as it gets: you have a bucket with a toilet seat attached to it. Add your bulking material as you go and when it gets full, you need to dump it somewhere. The best option we have found for this is to get a big plastic barrel with a lid that can be sealed. Put the contents of your bucket in the barrel and when it fills up, seal it and start another barrel. Let sealed barrels sit for a year to digest and after that, you’ll have perfectly usable compost.

Composting toilets, no matter what kind you have, are a little more hands-on than conventional ones, which can turn people off. Of course, some are more hands-on than others. All for the sake of saving water. It can be argued that the composting toilet gives you access to the end product which you can then use to grow plants. A conventional toilet hooked up to a septic system will end up putting the materials back in the ground, but you don’t get to put those materials anywhere you want. If you live in the city, well, your crap just ends up in the sewer and eventually the sewage treatment plant. Who knows what happens to it there. I can probably guess they aren’t growing plants with it, though it would be really awesome if they did. Unfortunately, a lot of people like to flush things down the toilet that they shouldn’t.

Let’s consider the toilet situation in a conventional Earthship. Water in an Earthship is used several times. It’s first use is when you take a shower, do your laundry or wash the dishes. As the water goes down the drain, it is sent through the planters in the greenhouse at the front of the house. At the end of the greenhouse, there is a small well where water that has traveled the length of the garden will gather there. That was two uses, if you’re keeping count: once for the initial washing, then feeding your plants.

The water that gathers in that well I just mentioned is the water that is used to flush your toilet, so you aren’t using fresh water for flushing, you’re using your grey water after it has been filtered by the plants. That’s usage number three of the same water you used to do your dishes. With this system, you get all of the ease-of-use and benefits of the conventional, low-flush toilet, but you aren’t using any fresh water to make it work. You will still need a septic tank, which people who use composting toilets will say is one of the benefits of them: you don’t need to spend several thousands of dollars putting in a septic system to use a composting toilet.

You don’t have hands-on access to the effluent that comes out of the septic tank, like you do having access to the output of your composting toilet, however you can still use it to grow plants if you put a botanical cell between the output of your septic tank and the leech field. This works great in the desert to create lush jungles around your house, however up here in Canada, it would only be a seasonal thing as the ground is frozen for half the year.

In the end, having and using a composting toilet seems mainly focused on saving water. In some places, this is an absolute necessity and so are highly suitable for those locations. But depending on the style of composting toilet you have, it may be using way more power than a conventional toilet so it is a debatable to say that they are really more environmentally friendly.

All I can say about ours, is if we were to do it all over again, we probably wouldn’t buy the expensive, fancy plastic version. It’s way cheaper and easier to build your own and you don’t have to worry about parts breaking that you can’t replace.


3 thoughts on “A few words about composting toilets”

  1. Wow, you could write a book! A very good read! I now know a lot more than I used to about the topic, but I can’t help but wonder …will there be a test. All in all, quite fascinating.
    Mums in AZ

    1. There will only be a test if you ever find yourself faced with having to acquire and use a composting toilet. We went with the ‘trial by fire’ method, though ultimately, it wasn’t a huge risk. I suppose for many things that is the only way to really learn about it: through experiencing it.

  2. There is one key factor that neither your post nor mine (done some months ago) took into account…





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