Building Materials Household & Appliances Waste & Recycling Water

Composting toilets: how they work

Have you ever wondered why we use manure to fertilize the soil and produce energy while human waste is only polluting the water and soil? Well, that’s because the toilets we use are not able to properly compost human waste. Wastewater from our toilets is normally conducted to water treatment plants through a sewage network as we explained in this post.

Although this sewage system works well in most urban areas, there are a number of reasons why you may not use it. Firstly, it may not be available in your location either because you are living in a non-served area, building a new home or camping. Secondly, you may want to take advantage of composting toilets to produce fertilizer for your garden. And lastly, you may want to reduce your impact on the environment as water treatment is often powered by polluting non-renewable sources of energy.

Portable toilets in shop at exhibition

Composting is the process of decomposing organic material through microorganisms that break it down into an odourless fertilizing material when exposed to a balanced environment in terms of oxygen, moisture and temperature. Since regular toilets are used for both urine and faeces and are full of water, composting can never happen there. Also, if waste is not flushed immediately, bad microorganisms start to proliferate causing bad smell.

A good composting toilet has a simple mechanism to separate toilet paper and faeces from urine so moisture can be more easily controlled. Our faeces are actually made up of 75% water and only 25% solid material and to help the evaporation process, composting toilets also need to be connected to a simple ventilation system. A manual handle usually operates a rotating drum or agitator to improve aeration.

In this video, you can see Bill Gates drinking water evaporated and treated from faeces by a process developed in partnership with Bill and Melinda Gates Foundation.


Most composting toilets will have a container to collect all the urine which can be as simple as a plastic bottle. This urine can be used to fertilize the soil. It just can’t be used directly on the leaves as it may burn them and it is also advisable to dilute at 10:1 ratio of water/urine at least, especially for young and delicate plants.

The compartment for faeces should be partially filled with damp coconut fibre, peat moss or sawdust. Make a layer of at least 8 cm at the bottom and cover with a thin layer after each time you use it. Some toilets may need to have their rotating system used from 3 times a week up to once a day.

Some composting toilets will have a separate drawer where the solid material can stay longer for composting, which avoids contamination from fresh waste when emptying it. If your composting toilet does not have this compartment or you are making your own, you can dump the waste in a composting bin and let it compost for nine to twelve months in total until it is safe to be used as a fertilizer. For more tips on how to make and use a compost bin read our post on home composting. You may also want to accelerate the process by building a wormery.

On this ABC News story, you can hear from some people that have adopted composting toilets in their homes.

When considering a composting toilet for your home, boat or camp, don’t forget to analyse how you will dispose of the final material and which features are more compatible for your use. If you are not able to have a composting toilet in your home, you can still help by saving water with our tips here and Green It Yourself Now!


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