All About Composting Toilets – 9 Things You MUST KNOW

Composting toilets are not widely used but the eco-friendly concept is sound.

We’ll break down how these toilets work today so you can see for yourself if you’d consider adding one to an off-grid holiday home.

First thing’s first, what are they exactly?

What Is a Composting Toilet?

This type of toilet treats human waste through the biological process of composting along with evaporation.

Since waste entering a toilet is composed of roughly 90% water, this is evaporated and carried back into the atmosphere through the venting in place.

The solid material remaining – and there won’t be much – is then converted to fertilizing soil through the process of natural decomposition.

How do composting toilets actually work, though?

When you first consider these waterless toilets, it can be baffling to understand how waste can be handled with all of the smell removed in the absence of water.

Why no water, though?

With the average American using 74 gallons of water each day, a composting toilet could save 6600 gallons of water per person per year.

Also, less energy is expended down the line from the septic system on to the treatment plant.

We’ll double down on that in a little more detail now and see how the mechanics make this composting treatment possible.

How Do Composting Toilets Work?

The process that makes this waste treatment possible is fundamentally the same as what takes place in a garden composter.

With oxygen, heat, water and organic material in the correct proportions, aerobic bacteria get the environment they need to turn waste into soil that can be used for fertilizing purposes.

When it’s broken down properly, no pathogens or viruses can remain in human waste. Those aerobic bacteria destroy these completely. Since it’s perfectly safe when fully decomposed, you can use the fertilizing soil to help reduce reliance on commercial fertilizers.

All composting toilets need to perform 3 core functions:

  1. Compost all waste along with toilet paper quickly, efficiently and without any odor
  2. Ensure that your finished compost is completely safe and straightforward to handle
  3. Evaporate all liquid during the process

Many composting toilets make use of carbon additives. Common examples include:

  • Coconut coir
  • Peat moss
  • Sawdust

These additives will help create air pockets in the waste. This facilitates aerobic decomposition.

You won’t need a connection to a sewer system or a septic tank.

Main Components

The toilet itself consists of 2 main units:

  • A place to sit
  • A collection unit

The collection unit can be subdivided into 4 key components:

  • Storage chamber: This is where the waste itself is kept. This area serves as a space for the waste to start breaking down into stable organic compounds. Usually slightly sloped, urine and solid waste are more easily separated
  • Ventilation unit: Within this area, degradation can take place aerobically and smelly gases properly vented
  • Mechanism for leachate management: Urine is diverted so excess liquid doesn’t interfere with decomposition
  • Access door for compost removal: Obviously, you’ll need access to get the waste out once properly decomposed

With that basic process outlined, how about decomposition?

How Does Decomposition Occur?

Firstly, most but not all of the liquid is evaporated.

90% of all human waste is water as we mentioned. When the urine in the composting chamber is diverted, this evaporated swiftly. It’s sent out into the air through the venting system.

The compost should not be totally dry, though. This is because decomposition calls for 4 key elements:

  • Moisture
  • Heat
  • Oxygen
  • Aerobic bacteria

Without at least a little moisture, the process falls down.

When all these elements occur in the correct mixture, decomposition takes place and the end result is soil that can be easily and safely used for fertilizing.

So, is this the type of toilet you’d install at home?

Main Applications for Composting Toilets

The primary use case for a composting toilet is any location without access to a water supply or sewage treatment.

Many rural areas and parks fall under this umbrella along with off-grid fishing cabins and holiday cottages out in the woodland.

Eco-tourism resorts often and understandably use these green and dry toilets.

Composting toilets are also common in developing countries so you might very well encounter one on your travels.

It’s perfectly possible to use a composting toilet for residential applications, too.

So far, so good.

How, though, is the end product actually used in real-world applications?

How Can The Compost Be Used?

The decomposed waste ends up with the texture of humus.

When used in a residential property, the compost is normally used in the garden. In terms of quality, it can easily rival store-bought compost. Indeed, the nutrient quantity and quality is often higher so don’t think of it as a subpar alternative.

What Regulations Are In Place for Composting Toilets?

The ISO is drafting a standard for composting toilets.

In the US, there are no universally accepted performance standards for these toilets.

The EPA does not have jurisdiction over the waste produced as long as it’s not referred to as fertilizer.

Regulation of these toilets takes place at state level.

What Makes Composting Toilets So Environmentally-Friendly?

Firstly, waste is not typically disposed of in a way that could degrade the environment. This alone make a decent impact.

Beyond this, no water is used for disposal.

There’s no water wasted during flushing. Even with water-efficient toilets – more on those next week – large volumes of water are used. Dry composting toilets use none.

Also, no potentially harmful chemicals are needed in conventional sewer lines since the waste doesn’t travel that route.


Whether you want a composting toilet at home or for an isolated off-grid second property, you’ve now got a thorough overview of how they work and what makes them so eco-friendly.

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