How to Use a Composting Toilet to Save Water and Fertilize Your Garden

How to Use a Composting Toilet to Save Water and Fertilize Your Garden

What is a Composting Toilet?

A composting toilet is a waterless, dry toilet that treats human waste by composting it. Unlike a flush toilet that uses several gallons of water to flush waste into a sewer system or septic tank, composting toilets use little to no water and convert waste into usable compost.

The toilet consists of a regular toilet seat and bowl, but under that is a chamber where waste collects. Instead of flushing, a continuous airflow dries and decomposes the waste. The end result is a useable compost that can fertilize non-edible plants, flowers, trees and lawns.

Composting toilets provide an eco-friendly alternative to conventional flush toilets. They conserve water, recycle nutrients, and can be used off-grid without sewer or septic systems.

How Do Composting Toilets Work?

Composting toilets work by leveraging natural biological processes to break down human waste into compost. Here’s an overview of how they work:

  • Deposit: Waste is deposited into the main chamber through the toilet seat. Urine flows through a separate diverter into a different holding tank.

  • Decompose: Continuous airflow circulates through chambers below the main tank, drying and decomposing the waste. Beneficial microbes, fungi and bacteria thrive in the warm, moist environment, breaking down waste and pathogens.

  • Convert: Over time (usually several months), waste is converted into a safe, useable compost. Some toilets have mechanisms to agitate or stir the compost to speed decomposition.

  • Remove: Finished compost can be manually removed via slide-out bins, raked out through a side access door, or emptied from an access hatch beneath the toilet.

  • Use: Mature compost can be used to fertilize non-edible plants, trees or lawns, completing the cycle.

Benefits of Composting Toilets

Composting toilets offer many advantages over conventional flush toilets:

Save Water

  • On average, flush toilets use 1.6 gallons of water per flush. Composting toilets use no water to process waste.
  • This saves thousands of gallons per year for an average household. Great for drought-prone areas.

Generate Compost

  • Waste is converted into a usable, nutrient-rich fertilizer instead of just “wasting it.”
  • Compost improves soil health and reduces need for chemical fertilizers.

Work Off-Grid

  • Composting toilets don’t require any energy or water lines. They work completely off-grid with no plumbing needed.
  • Ideal for remote cabins, tiny homes, or anywhere lacking sewer and septic access.

Lower Environmental Impact

  • No need for sewer lines, septic tanks, or wastewater treatment. Reduces infrastructure and energy usage.
  • Prevents wastewater pollution and eutrophication of waterways.

Save Money

  • Eliminates monthly water/sewer bills, septic pumping, and treatment costs.
  • Compost is a free, organic fertilizer for your garden.

Types of Composting Toilets

There are a few main types of composting toilets to choose from:

Self-Contained Units

These all-in-one units contain the toilet, composting chamber, leachate tank, and ventilation system in a single piece of furniture:

  • Low-maintenance and easy to use.
  • Ideal for RVs, tiny homes, and residential bathrooms.
  • More expensive than other designs.
  • Limited capacity.

Central Composting Units

The toilet seat and bowl are separate from the composting chamber located elsewhere:

  • Toilet can look like a normal flush toilet.
  • Allows for a much larger composting capacity.
  • Requires installation of waste pipes to connect toilet to chamber.

Urine-Diverting/Split Toilets

Urine is diverted to a separate holding tank while feces fall into the composting chamber:

  • Improves the composting process and quality of end product.
  • Requires second tank for urine waste.
  • Most eco-friendly option.

Batch-Style Toilets

Waste collects in removable bins within the toilet seat itself:

  • Very simple, low-cost design.
  • Bins must be frequently emptied or rotated.
  • Most basic and least efficient design.

Choosing the Right Composting Toilet

Consider the following when selecting a composting toilet:

  • Number of users – More users require a larger capacity.

  • Electricity access – If off-grid, avoid electric fans and heating coils.

  • Climate – Colder climates may require insulated tanks and passive solar heating.

  • Maintenance – Some are more hands-on than others.

  • Aesthetics – Self-contained units often look nicer than DIY models.

  • Budget – Prices range from $500 – $3000 USD. DIY can be much cheaper.

I recommend researching manufacturers like Nature’s Head, Sun-Mar, and Separett to compare different composting toilet models.

Ideal Conditions for Composting Toilets

Composting toilets require certain conditions to work effectively:

  • Warm, moist environment between 90-140°F accelerates composting.
  • Good airflow is critical – both passive and forced ventilation.
  • Correct carbon/nitrogen balance. Bulking agents like sawdust help.
  • Frequent rotating or agitation of compost speeds decomposition.
  • 2:1 mix of feces and bulking agent is optimal.
  • Urine diversion improves compost and prevents excess moisture.

Maintaining proper conditions prevents issues like odor and slow composting.

Using Compost from a Composting Toilet

The compost from a composting toilet can safely be used to fertilize non-edible plants, provided proper conditions are maintained. Here are some guidelines:

  • Allow compost to age at least a year after last addition.
  • Only apply compost to ornamental plants, not food crops.
  • Wear gloves and wash hands after handling finished compost as a precaution.
  • Compost is nutrient-rich – use like any other compost/fertilizer.
  • Composting toilet compost is safe, but perception may deter some vegetable gardeners.
  • Disinfect tools used to handle compost to prevent any potential pathogen transfer.
  • Compost is safe for mature trees, shrubs, flowers, lawns – great for landscaping.

In summary, composting toilet waste makes an excellent fertilizer for non-edible landscapes when properly aged and handled. It’s a sustainable way to “close the loop” and utilize the nutrients in human waste.


Composting toilets provide an eco-friendly, water-conserving alternative to wasteful flush toilets. When properly maintained, they generate a useful compost product from human waste. This compost can fertilize ornamental plants, trees, shrubs, and lawns. Composting toilets work completely off-grid, saving water, money, and reducing environmental impact. With the right model and conditions, they offer a sustainable solution for residential or commercial bathrooms.