Low-flush Toilets

Compiled by:
Beat Stauffer (seecon international gmbh)

Executive Summary

A low-flush or low-flow toilet is a flush toilet that is adapted in order to use significantly less water than a full-flush toilet. Low-flush toilets use a special design of the cistern and the siphon in order to allow the removal of faeces and excreta with less water. Most often, they also include a dual flush system, with one flush being designed for urine only, using even less water than the other designed for faeces. Today, there exist many suppliers of different models of low-flush toilets all over the world. Low-flush toilets reduce the water consumption, however, low-flush toilet still require large amounts of fresh water and with certain models, users have to flush even twice in order to achieve the complete removal of faeces from the bowl.

In Out

Freshwater, Urine or Yellowwater, Faeces, Excreta

Blackwater

Basic Design Principles

Low-flush toilets work with a very small amount of water. The exact amount of water varies between less than a litre (for urine only) up to 6 or 8 litres. These toilets can operate by gravity or vacuum. You can read more on vacuum toilets here. Gravity toilets have special requirements regarding the slope of the pipe. Large water savings are thus possible, which even facilitate the source separation of greywater and blackwater. If the gradient to the public sewer systems is steep enough, low-flush toilets can also be retrofitted into existing buildings. However, there is a risk of pipe clogging (HEEB et al. 2007).

In some cases, the volume of water used per flush is not sufficient to empty the bowl and consequently the user is forced to use two or more flushes to adequately clean the bowl, which negates the intended water saving (TILLEY 2008). Thus, many users were disappointed and frustrated with performance problems of the first generation of low-flush toilets. Since  then, the manufacturers have solved these problems by modifying passageways to move a reduced amount of water more vigorously around the bowl. To make these toilets even more efficient, dual-low-flush toilets where developed. This type of toilet saves water by offering different flush volumes: a full-flush for solids (faeces) and a half-flush for liquids (urine) (JCSA n.y.).

  ROUS WATER (2011)

With a toilet dual flush button, users have the possibility to choose between two volumes either for solids or for liquids. Source: ROUS WATER (2011)

 

 

 

Nowadays, products vary in that they may have narrower bowls with a smaller water surface, manually controlled water flow (via a foot pedal) into the bowl, or water pumps to assist in bowl emptying and cleaning. One model eliminates the “S” trap of a conventional toilet design, enabling waste to be washed down using less water. Another product flushes by opening a hinged flap to let wastes and a small amount of water fall into a lower chamber. After several seconds the flap reseals, and a blast of compressed air forces the wastewater over the trap and out a discharge line from the toilet (PIPELINE 2000).

Drain Lines

      PIPLINE (2000)

This low-flush toilet from Microphor in Willits, California, uses approximately 4.8 litres of water per flush. Source: PIPLINE (2000)

There are discussions about the performance of low-flush toilets to transport the waste trough the building drains to the public sewer system. As already mentioned, there is a risk of pipe clogging. Especially in older buildings, drain lines (slope, diameter, length) were designed for common flush toilets. More information and researches can be found in the document “Evaluation of Low-Flush-Volume Toilet Technologies to Carry Waste in Drain lines” (GAULEY and KOELLER 2005).

     


Reuse of Faecal Sludge as Fertiliser

The toilet waste or blackwater (urine and faecal matter) contains the majority of the nutrients in wastewater. A century ago, toilet waste was collected in major European cities and used as fertiliser in near urban agriculture. Ordinary flush toilets use much water and the blackwater becomes diluted. Modern toilet technology (vacuum or low-flush gravity) have flush volumes below 1 litre. With these toilets collection and separate treatment of the concentrated blackwater is more interesting in order to treat and reuse it (JENSSEN et al. 2004).

Costs Considerations

Costs are not higher than a common flush toilet system. But the huge savings of flush water and the smaller volume of generated blackwater reduce operation costs significantly.

Operation and Maintenance

Although flushing water rinses the bowl, the toilet should be scrubbed clean regularly. It is important that no other object than faeces or urine are tried to flush away, because in this case the risk of clogging is even higher and could lead to expensive cleanout costs.

Health Aspects

The low-flush toilet itself is safe and comfortable to use provided it is kept clean. There are no real problems with odours if used correctly (TILLEY et al. 2008). If the flush performance is bad, the bowl should be cleaned more often. Furthermore, in the absence of an appropriate (semi-)centralised treatment system, toilet wastewater flows through a sewer system directly into the environment without any treatment. This spreads pathogens and can endanger the health of residents (see also health and hygiene issues).

At a Glance

Working Principle

Human excreta is flushed away by a minimised amount of water.

Capacity/Adequacy

Basically, it can be built everywhere, urban and rural areas. A constant source of water and an appropriate sever system and (semi-)centralised treatment system must be available.

Performance

Depends on type, but there are many models with a high performance available.

Costs

Not higher than a common flush toilet system. Minimised flushed water and blackwater reducing operation costs.

Self-help Compatibility

Low, it might be difficult to find spare parts.

O&M

Easy to use and clean. Beside human excreta and toilet paper, no other objects should be flushed.

Reliability

If well maintained and constructed, high.

Main strength

Comfortable and hygienic for the user. Saves large amounts of water in comparison with common flush-toilets.

Main weakness

Still requires water. The risk of water pollution in sequence of unprofessional wastewater discharge is high.

Applicability

A flush toilet should not be considered unless all of the connections and hardware accessories are available locally. The low-flush toilet must be connected to both a constant source of water (can be a big problem and controversy in arid climates) for flushing and a collection and storage/treatment or conveyance technology to receive and treat the blackwater. The flush toilet is suitable for both public and private applications and can be used in every climate (TILLEY et al. 2008).

Advantages

  • Ultra-low-flow toilets reduce water consumption and costs to the consumer
  • They contribute to preserving the environment by protecting ground water from depletion and possible contamination
  • Easy to use and clean

Disadvantages

  • Some ultra-low-flow models may require flushing more than once to adequately clean the toilet bowl
  • Risk of clogging/plugging
  • It still requires a constant source of water, it will not function without it

References Library

JENSSEN, P.D.; GREATOREX, J.M.; WARNER, W. S. (Editor) (2004): Sustainable Wastewater Management in Urban Areas. (= Kapitel 4. Kurs WH33, Konzeptionen dezentralisierter Abwasserreinigung und Stoffstrommanagement). Hannover: University of Hannover.

HEEB, J.; JENSSEN, P.; GNANAKAN, K.; CONRADIN, K. (2007): M3: Ecosan Systems and Technology Components. M 3-2: Ecosan Technologies to Close the Water Loop. In: HEEB, J.; JENSSEN, P.; GNANAKAN; CONRADIN, K. (2008): Ecosan Curriculum 2.3. Switzerland, India and Norway.

GAULEY, B.; KOELLER, J. (2005): Evaluation of Low-Flush-Volume Toilet Technologies to Carry Waste in Drain lines. Final Report. Mississauga and Yorba Linda: Veritec Consulting and Koeller and Company. URL [Accessed: 14.03.2011].

JCSA (Editor) (n.y.): WaterSense High-Efficiency Toilet Guide. Williamsburg: James City Service Authority (JCSA). URL [Accessed: 14.03.2011].

PIPELINE (Editor) (2000): Alternative Toilets Options for Conservation and Specific Site Conditions. Morgantown: National Small Flows Clearinghouse. URL [Accessed: 25.05.2011].

ROUS WATER (Editor) (2011): Dual Flush Toilet Rebates. Lismore: Rous Water. URL [Accessed: 15.03.2011].

TILLEY, E.; LUETHI, C.; MOREL, A.; ZURBRUEGG, C.; SCHERTENLEIB, R. (2008): Compendium of Sanitation Systems and Technologies. Duebendorf, Switzerland: Swiss Federal Institute of Aquatic Science and Technology (EAWAG) and Water Supply and Sanitation Collaborative Council (WSSCC). URL [Accessed: 15.02.2010].

See document in FRENCH

Further Readings Library

Reference icon

CORCORAN, E. (Editor); NELLEMANN, C. (Editor); BAKER, E. (Editor); BOS, R. (Editor); OSBORN, D. (Editor); SAVELLI, H. (Editor) (2010): Sick Water? The central role of wastewater management in sustainable development. A Rapid Response Assessment. United Nations Environment Programme (UNEP), UN-HABITAT, GRID-Arendal. URL [Accessed: 05.05.2010].

This book not only identifies the threats to human and ecological health that water pollution has and highlights the consequences of inaction, but also presents opportunities, where appropriate policy and management responses over the short and longer term can trigger employment, support livelihoods, boost public and ecosystem health and contribute to more intelligent water management.


Reference icon

HEEB, J.; JENSSEN, P.; GNANAKAN, K.; CONRADIN, K. (2007): M3: Ecosan Systems and Technology Components. M 3-2: Ecosan Technologies to Close the Water Loop. In: HEEB, J.; JENSSEN, P.; GNANAKAN; CONRADIN, K. (2008): Ecosan Curriculum 2.3. Switzerland, India and Norway.

This presentation is adapted from the Ecosan Curriculum 2.2. The ecosan curriculum was created in order to compile the large amount of information on ecological sanitation in a structured and comprehensive way. This is a summary about the various Ecosan (or more: sustainable sanitation) systems.


Reference icon

GAULEY, B.; KOELLER, J. (2005): Evaluation of Low-Flush-Volume Toilet Technologies to Carry Waste in Drain lines. Final Report. Mississauga and Yorba Linda: Veritec Consulting and Koeller and Company. URL [Accessed: 14.03.2011].

This study researches if the minimised amount of water from low-flush toilets is able to carry waste in drain lines.


Reference icon

JCSA (Editor) (n.y.): WaterSense High-Efficiency Toilet Guide. Williamsburg: James City Service Authority (JCSA). URL [Accessed: 14.03.2011].

This guide mentions all important points if someone wants to buy a low-flush toilet.


Reference icon

JENSSEN, P.D.; GREATOREX, J.M.; WARNER, W. S. (Editor) (2004): Sustainable Wastewater Management in Urban Areas. (= Kapitel 4. Kurs WH33, Konzeptionen dezentralisierter Abwasserreinigung und Stoffstrommanagement). Hannover: University of Hannover.

A document about sustainable wastewater management in urban areas.


Reference icon

PIPELINE (Editor) (2000): Alternative Toilets Options for Conservation and Specific Site Conditions. Morgantown: National Small Flows Clearinghouse. URL [Accessed: 25.05.2011].

This article describes some alternative toilet systems


Reference icon

WOSTMAN (Editor) (2010): EcoFlush Urine Separating Toilet. Saltsjoe-Boo: Wostman Ecology AB. URL [Accessed: 16.03.2011].

This paper introduces a urine separating low-flush toilet.


Reference icon

WHO (Editor) (2006): Guidelines for the safe use of wastewater excreta and greywater. Volume IV. Excreta and Greywater Use in Agriculture. Geneva: World Health Organisation. URL [Accessed: 26.02.2010].

Volume IV of the Guidelines for the Safe Use of Wastewater, Excreta and Greywater recognizes the reuse potential of wastewater and excreta (including urine) in agriculture and describes the present state of knowledge as regards potential health risks associated with the reuse as well as measures to manage these health risks following a multi-barrier approach.


Reference icon

TOUBKISS, J. (2010): How to Manage Public Toilets and Showers. (= Six Methodological Guides for a Water and Sanitation Services' Development Strategy, 5). Cotonou and Paris: Partenariat pour le Développement Municipal (PDM) and Programme Solidarité Eau (pS-Eau). URL [Accessed: 19.10.2011].

The purpose of this decision-making aid is to provide practical advice and recommendations for managing toilet blocks situated in public places. It is primarily aimed at local decision-makers in developing countries and at their partners (project planners and managers).

See document in FRENCH


Case Studies Library

Reference icon

ATLANTIC ECOWORKS (Editor) (n.y.): Case Study 4. Dual-Flush Toilet. Charlottetown: Atlantic EcoWorks. URL [Accessed: 15.03.2011].

This case study estimates the annual water consumption and savings that can be realised by a family of four using a dual-flush toilet instead of a conventional 13-litre or 6-litre toilet.


Important Weblinks

http://www.youtube.com/ [Accessed: 15.03.2011]

This short video shows the performance of a low-flush toilet.

http://www.savewaterproject.com/ [Accessed: 16.03.2011]

On this website, several low-flush toilets are described.

http://www.flushmate.com/ [Accessed: 16.03.2011]

The “How it Works” section of the company FLUSHMATE explains the flush system of its low-flush toilets.

http://abettertoilet.org/ [Accessed: 23.11.2013]

The sanitation technology paradigm is under review, as past approaches are not sufficient or affordable to close the sanitation coverage gap. In 2011, the Bill & Melinda Gates Foundation (BMGF) launched the bold Reinvent the Toilet Challenge (RTTC) program to promote the development of radically new innovations to address the sanitation challenge on a large-scale. The RTTC is premised on the fact that ground-breaking improvements are required in toilet design and fecal sludge management to close the urban sanitation gap. The RTTC is focused on reinventing the flush toilet, a break-through public health invention that has not changed substantially since the first flush toilet patent was issued in 1775.