How Does a Dry Toilet Work?

While pressing a button and watching water flow down the toilet is an everyday action we have normalized, the reality is that the invention of the water-based toilet is relatively recent. In fact, many of our grandparents still remember the classic communal outhouses in villages where a simple shared hole served an entire neighborhood.

Today, having a dry toilet at home may seem eccentric—something for hippies or eco-radicals—but the reality is that dry toilets have been modernized, and there are distributors of high-tech systems where, if we weren’t told, we wouldn’t realize they are waterless bathrooms.

These are the new dry toilets, an increasingly popular option among clients who want to build ecological and self-sufficient homes. The water consumption of a conventional toilet can represent up to 40% of a household’s total water usage.

For this reason, in today’s article we discuss this toilet system that does not require water to function. Yes, you read that correctly! These toilets do not need any connection to the water supply. But that’s not all—they also do not need to be connected to the public sewage system. Therefore, they can save us a great deal of money on water consumption and, in the process, generate very practical compost if we have a garden or vegetable patch.

We will begin with a general description of what a dry toilet is and how it works, followed by an analysis of its uses and benefits in the domestic setting.

Next, we will update you on its availability in the current market: where we can purchase them, what prices they have, etc.

Finally, to show you that the dry toilet is a genuine investment for the future, we will explain a practical case or example of a passive house that uses dry toilets in all its bathrooms.

How Does a Dry Toilet Work?

The dry toilet, or composting toilet, is a type of dry sanitation system. That is, it functions without the need for water for waste disposal.

They can be used independently of water supply and sewage connections and provide a safe and hygienic sanitation alternative, whether we want a self-sufficient home or find ourselves in an area without conventional sanitation infrastructure.

In this way, the dry toilet can help us significantly reduce household water consumption and wastewater treatment costs.

The dry toilet separates feces and urine from common wastewater. Plant nutrients and organic matter are recycled through composting, and the remaining domestic wastewater can be treated more easily.

In this manner, composting toilets act as local pretreatment systems, retaining substances that can be harmful to the environment.

Although a commitment is required from users and operators to maintain the system properly—including handling fecal compost—this maintenance is minimal. Depending on the technology, it may involve emptying once a year or, depending on usage, every two years of an odorless material rich in minerals and nutrients for the garden.

For the most part, the dry toilet is a domestic system, easy to use and maintain, and can therefore be applied in most parts of the world, either as low-cost, self-built solutions or as manufactured, high-tech products.

Uses and Benefits of the Dry Toilet

Main Functions of the Dry Toilet

The dry toilet or composting (biological) toilet receives and processes excrement and toilet paper in a specially designed container or vault. Some systems combine the treatment of feces and urine in one vault, while others are specifically designed for the separate treatment of feces and urine.

Biodegradable household waste, including organic food waste, can also be added to the vault as it will biologically degrade in the composting process along with the feces.

The dry toilet consists of two basic elements: a seat or squatting platform and a collection or composting device. In addition, a ventilation system allows proper aeration of the composting vault and reduces odor.

The frequency of emptying the composting vault depends on the container’s capacity, the feeding rate, and the composting conditions.

The Composting Process:

During the composting process, organic matter is biologically degraded by thermophilic bacteria, fungi, and other soil bacteria such as actinomycetes.

Under optimal conditions, temperatures within the compost pile rise to between 50 and 70°C due to the biological activity of bacteria. Thanks to these elevated temperatures, the composting process itself can provide substantial and rapid pathogen reduction.

Realistically, it is difficult to achieve these optimal conditions constantly, but periodic maintenance can be performed to ensure proper functioning of the composting process and the dry toilet system in general.

Ventilation:

The composting container or vault is ventilated to improve both aeration and evaporation of excess moisture in the compost pile. In addition, ventilation systems allow us to control odors through negative pressure.

In more advanced cases, an electric fan with speed control is installed inside the vault. The fan helps balance toilet usage (if airflow is too strong) with odor control (if airflow is too low) and ensures that cooling and drying of the compost mass are avoided.

Other more economical alternatives may include wind-driven fans, pipe insulation, and passive surfaces heated by solar energy, but these are less controllable.

Hygiene and Domestic Maintenance:

At the domestic level, and especially to avoid unpleasant odors in the home, it is important to ensure that the chambers are built hermetically, leaving only two open access points: the toilet bowl and the upper outlet of the ventilation pipe.

With these two points in place, interior-to-exterior circulation occurs due to pressure differences, either through the suction effect caused by winds around the outlet, the chimney effect (warm air rises through the ventilation pipe), or atmospheric pressure differences due to greater height outdoors.

It is also important, as we mentioned earlier, to use the dry toilet correctly by covering and mixing feces with prepared soil after each use.

Current Market Offerings

There are many different types and models offered by manufacturers and distributors in many countries within a wide price range, depending on design complexity, the number of units required, transportation costs, production, and the economy.

First, we find standard or low-tech composting systems.

These are basically storage facilities where excrement is collected and left to decompose at room temperature. They may require more maintenance than semi-automatic systems and a greater degree of user involvement in the treatment process.

In contrast, high-tech composting systems or dry toilets are more compact units and are usually equipped with automatic mixers and thermostat-controlled heaters. They require less user intervention, provided the technical equipment functions reliably.

The dry toilet can also be self-built, provided the basic operating principles and construction technique are ensured.

Cost

Given the product offerings, we will also find differences in budgets depending on whether we are discussing a self-built, standard, high-tech, or low-tech dry toilet.

Construction costs for self-built toilets are usually lower than manufactured toilet systems, especially if local materials are used and labor costs are low. Owner-built toilets can be a good solution for low-income areas and locations without any other sanitation infrastructure.

On the other hand, standard or low-tech systems represent a higher investment compared to self-built ones but are always much less expensive than high-tech units.

Finally, high-tech composting toilet systems offer a good solution if space is expensive or limited and technical support is readily available, but they are logically the most expensive on today’s market.

Real-World Application

Composting toilet systems can be built simply, either manually or with more advanced technologies and mechanical processes.

Due to their main characteristic of dry operation, this type of installation is particularly suitable for arid areas or land without central water supply or sewage.

In some projects, dry toilets have been implemented in houses up to four stories high.

For proper operation and maintenance, a dry toilet requires commitment from users who will be responsible for managing the entire system.

In Sweden, for example, the Gebers collective housing project was built, consisting of apartment buildings for 80 residents.

All apartment bathrooms were equipped with urine-diverting dry toilet systems. Urine is collected in a collective tank in the basement and reused in agriculture after additional external storage.

On the other hand, feces fall directly into conventional 140-liter containers through pipes. The reduced size of the containers allows them to be transported and emptied regularly at a nearby composting site.