When deciding what capacity you need for your composting toilet system, consider:

• How many people will likely use the system every day?
• For large-capacity applications, also ask: How many people will use it every year?

Most manufacturers classify their models by how many people can use the system during a specific period of time and still have the system produce an acceptable end product. This classification takes into account the composter’s ability to contain and compost excrement and toilet paper, plus its ability to contain or evaporate excess leachate.

Caution: Before you buy a composting toilet system, you must understand the formula that each manufacturer uses to classify models. The formulas differ unless they were tested under a uniform performance standard, such as NSF/ANSI International Standard 41 or the basis for Product Label’s Nordic Environmental Labeling Criteria for Closed Toilet Systems.