The affirmative argument is that a dry toilet is safer, odor-free, sustainable, waterless, inexpensive, low maintenance, scalable from one unit to dozens. 

The counter argument that some people will make is that, at least in the U.S., it's been tried and doesn't work very well: Waterless, so-called composting toilets appeared during the 1960s. Eco-enthusiasts and counter-culturals began constructing and using simplistic designs.  Although well intentioned they had little basic knowledge and less ability to adapt and maintain their toilets in specific environments.  Such installations became smelly and fly-infested, causing people to dread using them, the owners to neglect their upkeep and ultimately to abandon them.

Where there has been especially strong need:  In many developing countries of the world there is little sanitation infrastructure and few resources to build it.  Various governmental and non-governmental organizations wanting to improve sanitation, water quality, and reduce health problems, have worked over the past 30-40 years to identify cost-effective toilet and sewage alternatives and launch projects to implement them.  (A survey of dry toilet projects in rural South Africa, rural areas of Kenya, places near Bolivian cities, rural households and schools in Central and Eastern Europe, and indoor installations in Sweden and Peru, is found here.)

(Photos: GIZ)

Although dry toilets have most recently been perfected as replacements for pit latrines in poor or developing countries, they are also ideal anywhere sewer systems and sludge disposal are dangerous or expensive to implement. To summarize, the benefits include:

• Low cost:  Studies show site-built dry toilets not only to be less expensive to build and maintain than flush-toilet systems with septic tanks, but also cheaper overall than pit latrines.
  
• Wide applicability:  The odor-free, pest-free and fly-free performance makes it suitable for both outdoor and indoor installations in most climates.
• Safe:  The dry conditions of fecal matter promote aerobic decomposition, and pathogens don't leach into the environment and groundwater.
• Relatively easy maintenance:  Emptying of fecal matter from dehydration containers is not offensive and relatively easy.
• Adaptable:  All kinds of user needs have been satisfactorily met through a variety of design innovations and tailored installations.

Local Conditions and Physical Site. If one or more of the following apply, you are a candidate for dry toilets:

• Need to improve the level of sanitation,
• Need to replace full, leaking, foul latrines,
• Deal with the problem of open sewage discharge,
• Stop contamination of ground water,
• Have limited water for toilet flushing,
• Have faulty septic tanks,
• Need to reduce operating costs and maintenance effort.
• Not have adequate sewage system or funds to build and maintain one,
• Find it too expensive to connect to existing waste-water treatment system,
• Have a need for inexpensive agricultural fertilizer or soil conditioning.

Summary of Basic Concept:  The term "dry toilet" can be interpreted in two ways: (1) no-flush toilet with urine and feces going down the chute to the same container, and (2) no-flush but urine is diverted from the feces container to a separate tank, container, soak hole or garden.  (A dry toilet would not involve a so-called lo-flush unit because, although much less water is used, the flush water would prevent the feces from drying out and could drown the aerobic bacteria (see Sanitation).

Regardless of what they are called (dry toilet, composting toilet, no-flush toilet, etc.) all of them reduce liquid in the collection chamber to a very minimum by not flushing with fresh water and by limiting or preventing urine from co-mingling with the feces.

Brief Description of Dry Toilet Operation:  Other pages on this website describe dry toilet operation in every detail, but here is a preview:

At this point the Urine Diversion Dehydration Toilet (UDDT, sometimes known as the ecosan toilet or the Double Vault Urine Diversion Latrine or DVUD latrine) is described. It is a dry toilet that separately collects urine and feces with a special toilet seat.

The UDDT takes advantage of the anatomy of the human body which excretes urine and feces independently allowing these to be collected separately. Urine is drained via a small hole at the front area of the toilet seat connected to a tube leading to a separate tank, while feces fall through a larger hole in the back directly into a vault or bin.

Urine is generally sterile and odorless when drained away in this fashion. It is high in nitrogen, potassium and phosphorus and an excellent fertilizer.

The user drops a cup or handful of dry covering material into the vault or bin through the feces hole after each defecation event. This covering material soaks up moisture, facilitates aeration, and provides carbon for aerobic bacteria. It controls initial odor, provides a barrier that keeps flies away and gets the feces largely “out of sight”.

Urine diversion and the absence of flush water keep the feces dry.  This virtually stops emission of nitrogen (ammonia), hydrogen sulfide (noxious odors), and methane (odorless greenhouse gas), promoting aerobic decomposition.  Dehydration is aided by a vent pipe.  As moisture is evaporated the contents shrink by up to fifty percent. 

Dry conditions over extended time (one year or more), plus moldering (Brit: mouldering) or composting action (depending on ambient temperatures and air circulation) destroy pathogens, mostly sanitizing the contents of bin or vault.

The crumbly, powdery, odorless humus that results is inoffensively and safely removed at intervals that depend on the capacity of bins.  It can be used as fertilizer and soil conditioner; however reuse is optional and, along with the urine, it can be safely disposed of on- or off-site.

Dry toilets can be purchased, ready-made, suitable for installation in certain circumstances, or they can be readily constructed on-site.