What do you picture when someone mentions a composting toilet? An old long-drop? Or a comfortable bathroom that saves water? If you've only come across the first, modern composting toilet systems may surprise you.
A composting toilet gives you a familiar toilet to use, with a biological treatment system taking care of the waste. Instead of using drinking-quality water to flush after every visit, it keeps the material in a chamber where composting can take place. For homes, baches and off-grid properties, that's a practical reason to consider one.
Your bathroom can look reassuringly normal, too. With a split system, the pedestal sits in the room while the composting chamber is underneath or beside the building. A self-contained system does its processing inside the on-floor unit. You still use a toilet; what changes is how the waste is treated afterwards.
A familiar toilet, a different way to treat waste
A composting toilet holds waste in conditions that help microorganisms break it down. Give that process enough chamber space, air, moisture and time, and you have the basis of a working treatment system. Those features are built into the toilet's design, rather than left for you to figure out from scratch.
So, how do composting toilets actually work?
Inside the chamber, microorganisms break down organic material with the help of oxygen. Human waste and toilet paper provide some of that material. The recommended carbon-rich bulking mix helps balance it and creates space for air to move. The vent, drainage and evaporation features then help maintain the conditions the compost needs.
- Airflow: the ventilation system supplies air and carries moisture and odour away from your bathroom.
- Moisture: compost needs to remain moist and aerated, rather than waterlogged or completely dry.
- Carbon and structure: the correct bulking material helps create air spaces and balances nitrogen-rich inputs.
- Temperature and time: your system needs to suit the local climate and hold material for its intended treatment period.
- Capacity: enough chamber volume and the right operating routine give the process room to work.
You don't need to keep experimenting with the mix. Follow your toilet's manual for what to add and how much, and use our Bulking Agents & Dosing Guide when choosing supplies. More water, more bulking material or more mixing isn't automatically better—the aim is to keep the balance right.
What is it like to use one?
For you and your visitors, the experience is much like using an ordinary toilet. Sit down, use toilet paper and follow the short instructions for your model. With many systems, you add a measured amount of bulking material instead of pressing a flush button. Others have a different dosing or mixing routine, so it's worth keeping the instructions handy for guests.
And no, choosing a composting toilet shouldn't mean putting up with a smelly bathroom. Correctly installed ventilation draws air in the right direction and out of the room. Our article Do Composting Toilets Smell? explains how that works, including what you might notice when opening a chamber for servicing.
Not every waterless toilet treats waste in the same way
For a permanent home, we favour systems designed to treat the waste within their own equipment. These include continuous composting chambers, batching systems that keep material in their purpose-designed chambers while it matures, and suitable processor systems with treatment and finishing stages.
A compact RV toilet may do a different job: separating urine and collecting solids until you can empty them. These can be excellent travel toilets, but collecting waste isn't the same as completing composting. If you're comparing one with a residential system, ask what treatment happens before emptying and what happens next. Simply adding an ordinary garden bin doesn't make an incomplete residential treatment arrangement compliant.
You may also see microbial additives listed in a toilet's instructions. Microorganisms are essential to composting, but that doesn't mean every design needs you to buy the same additive. Use the products specified for your model.
Where do the liquids and finished material go?
Some systems accept urine and solids together, managing liquids through evaporation and any drainage included in the design. Others divert urine into a separate container or drain. That separated urine is still untreated waste, so you need a suitable place for it to be received or treated.
When material is ready to come out, follow the handling and disposal instructions for your system and property. An earthy smell or soil-like appearance alone doesn't make it suitable for unrestricted garden use. New Zealand's requirements allow non-water-borne sanitation, but the way you manage and dispose of the waste must remain healthy and safe.
You'll also need to account for water from the shower, basins, kitchen and laundry. Choosing a composting toilet lets you consider the toilet waste separately from those flows, rather than assuming everything has to be managed in the same way.
A well-chosen composting toilet gives you a comfortable bathroom, saves flushing water and lets a managed biological process do the treatment work. The key is choosing enough system for your household and using it as designed.
Thinking about a composting toilet for your home?
Call us on 0800 022 027. Tell us how many people will use it, whether you have space below the floor and how the property is used. We can help you compare systems, with project-specific design consultancy available when needed.
