U.4 Flush Toilet

There are two types of Flush Toilets: the pour flush toilet, where water is poured in manually by the user, and the cistern flush toilet, where the water comes from a cistern above the toilet. A cistern flush toilet is directly connected to the water supply network. When the water supply is not continuous, any cistern flush toilet can become a pour flush toilet.User interface used for urination and defecation.

A Flush Toilet has a water seal that prevents odours and flies from coming up the pipe. For pour flush toilets, water is poured into the bowl to flush excreta away; approximately 1 to 3 L is usually sufficient. The quantity of water and the force of the water (pouring from a height often helps) must be sufficient to move excreta up and over the curved water seal. In cistern flush toilets, water is stored in the cistern above the toilet bowl and is released by pushing or pulling a lever. This allows water to run into the bowl, mix with the excreta, and carry it away. Alternatively water can be poured in manually using a bucket ( pour flush toilet). Both pedestal and squat toilets can be used. Due to demand, local manufacturers have become increasingly efficient at mass-producing affordable Flush Toilets.

Consists of urine and faeces that are not mixed with any flushwater. Excreta is relatively small in volume, but concentrated in both nutrients and pathogens. Depending on the characteristics of the faeces and the urine content, it can have a soft or runny consistency.Refers to (semi-solid) excrement that is not mixed with urine or water. Depending on diet, each person produces approximately 50–150 L per year of faecal matter of which about 80 % is water and the remaining solid fraction is mostly composed of organic material. Of the total essential plant nutrients excreted by the human body, faeces contain around 39 % of the phosphorus (P), 26 % of the potassium (K) and 12 % of the nitrogen (N). Faeces also contain the vast majority of the pathogens excreted by the body, as well as energy and carbon rich, fibrous material.The liquid produced by the body to rid itself of nitrogen in the form of urea and other waste products. In this context, the urine product refers to pure urine that is not mixed with faeces or water. Depending on diet, human urine collected from one person during one year (approx. 300 to 550 L) contains 2 to 4 kg of nitrogen. The urine of healthy individuals is sterile when it leaves the body but is often immediately contaminated by coming into contact with faeces.Any substance that is used for growth. Nitrogen (N), phosphorus (P) and potassium (K) are the main nutrients contained in agricultural fertilisers. N and P are also primarily responsible for the eutrophication of water bodies.
An organism or other agent that causes disease.User interface used for urination and defecation. The organic molecule (NH2)2CO that is excreted in urine and that contains the nutrient nitrogen. Over time, urea breaks down into carbon dioxide and ammonium, which is readily used by organisms in soil. It can also be used for on-site faecal sludge treatment. See. S.18

Design Considerations

The U-trap that facilitates the flush toilet water seal should be made out of plastic or ceramic to prevent clogs and to make cleaning easier (concrete may clog more easily if it is rough or textured). The shape of the water seal determines how much water is needed for flushing. The optimal depth of the water seal head is approximately 2 cm to minimise water required to flush the excreta. The trap should be approximately 7 cm in diameter. Modern cistern flush toilets use 6 to 9 L per flush, whereas older models were designed for flush water quantities of up to 20 L. There are different low-volume Flush Toilets currently available that can be used with as little as 1.5 L of water per flush. A plumber is required to install a Flush Toilet to ensure that all valves are connectedand sealed properly, therefore, minimizing leakage.

Consists of urine and faeces that are not mixed with any flushwater. Excreta is relatively small in volume, but concentrated in both nutrients and pathogens. Depending on the characteristics of the faeces and the urine content, it can have a soft or runny consistency.Refers to (semi-solid) excrement that is not mixed with urine or water. Depending on diet, each person produces approximately 50–150 L per year of faecal matter of which about 80 % is water and the remaining solid fraction is mostly composed of organic material. Of the total essential plant nutrients excreted by the human body, faeces contain around 39 % of the phosphorus (P), 26 % of the potassium (K) and 12 % of the nitrogen (N). Faeces also contain the vast majority of the pathogens excreted by the body, as well as energy and carbon rich, fibrous material.Water discharged into the user interface to clean it and transport the contents into the conveying system or to the on-site storage. Freshwater, rainwater, recycled greywater, or any combination of the three can be used as a flushwater source. Many sanitation systems do not require flushwater.Total volume of water generated from washing food, clothes and dishware, as well as from bathing, but not from toilets (see blackwater). It may also contain traces of excreta (e.g. from washing diapers) and, therefore, some pathogens. Greywater accounts for approximately 65 % of the wastewater produced in households with flush toilets.The liquid produced by the body to rid itself of nitrogen in the form of urea and other waste products. In this context, the urine product refers to pure urine that is not mixed with faeces or water. Depending on diet, human urine collected from one person during one year (approx. 300 to 550 L) contains 2 to 4 kg of nitrogen. The urine of healthy individuals is sterile when it leaves the body but is often immediately contaminated by coming into contact with faeces.Describes the type of toilet, pedestal, pan, or urinal that the user comes into contact with; it is the way users access the sanitation system. In many cases, the choice of user interface will depend on the availability of water and user preferences. Additionally, handwashing facilities have been included here with a dedicated technology information sheet as a constant reminder that each sanitation user interface needs to be equipped with handwashing facilities for optimal hygiene outcomes.A sanitation system is a multi-step process in which sanitation products such as human excreta and wastewater are managed from the point of generation to the point of use or ultimate disposal. It is a context-specific series of technologies and services for the management of these sanitation products, i.e. for their collection, containment, transport, treatment, transformation, use or disposal. A sanitation system comprises functional groups of technologies that can be selected according to context. By selecting technologies from each applicable functional group, considering the incoming and outgoing products, and the suitability of the technologies in a particular context, a logical, modular sanitation system can be designed. A sanitation system also includes the management and operation and maintenance (O & M) required to ensure that the system functions safely and sustainably. Any substance that is used for growth. Nitrogen (N), phosphorus (P) and potassium (K) are the main nutrients contained in agricultural fertilisers. N and P are also primarily responsible for the eutrophication of water bodies.
An organism or other agent that causes disease.The means of safely collecting and hygienically disposing of excreta and liquid
wastes for the protection of public health and the preservation of the quality of public water bodies and, more generally, of the environment.

User interface used for urination and defecation. The organic molecule (NH2)2CO that is excreted in urine and that contains the nutrient nitrogen. Over time, urea breaks down into carbon dioxide and ammonium, which is readily used by organisms in soil. It can also be used for on-site faecal sludge treatment. See. S.18Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.

Materials

Cistern flush toilets are typically made of porcelain and are a mass-produced, factory-made user interface. Squatting slabs can be made locally with concrete (providing that sand and cement are available), fibreglass, porcelain or stainless steel. Wooden or metal moulds can be used to produce several units quickly and efficiently. Prefabricated pedestals and squatting slabs made from plastic are also available, as are water seal devices that can be attached to squatting slabs.

Describes the type of toilet, pedestal, pan, or urinal that the user comes into contact with; it is the way users access the sanitation system. In many cases, the choice of user interface will depend on the availability of water and user preferences. Additionally, handwashing facilities have been included here with a dedicated technology information sheet as a constant reminder that each sanitation user interface needs to be equipped with handwashing facilities for optimal hygiene outcomes.A sanitation system is a multi-step process in which sanitation products such as human excreta and wastewater are managed from the point of generation to the point of use or ultimate disposal. It is a context-specific series of technologies and services for the management of these sanitation products, i.e. for their collection, containment, transport, treatment, transformation, use or disposal. A sanitation system comprises functional groups of technologies that can be selected according to context. By selecting technologies from each applicable functional group, considering the incoming and outgoing products, and the suitability of the technologies in a particular context, a logical, modular sanitation system can be designed. A sanitation system also includes the management and operation and maintenance (O & M) required to ensure that the system functions safely and sustainably. The means of safely collecting and hygienically disposing of excreta and liquid
wastes for the protection of public health and the preservation of the quality of public water bodies and, more generally, of the environment.

User interface used for urination and defecation. Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.

Applicability

A Flush Toilet is only appropriate where a constant supply of water is available. The water does not need to be of drinking quality. Greywater can be recycled for flushing. The amount of organics and pathogens should be small, in order to prevent piping from clogging due to the growth of biofilm and to prevent user exposure to pathogens. The Flush Toilet is appropriate for those who sit or squat (pedestal or slab), as well as for those who cleanse with water or toilet tissue. The pour flush toilet requires (much) less water than a cistern flush toilet. However, because a smaller amount of water is used, the pour flush toilet may clog more easily and, thus, require more maintenance. Generally, pour flush is most suitable for pit or offset pit toilets and possibly Septic Tanks S.13 close to the toilet. A cistern flush toilet should only be considered if all of the connections and hardware accessories are available locally. If water is available, this type of toilet is appropriate for both public and private applications. Flush toilets must be connected to a collection and storage/treatment or conveyance technology to receive the blackwater.

Mixture of urine, faeces and flushwater along with anal cleansing water (if water is used for cleansing) and/or dry cleansing materials. Blackwater contains the pathogens, nutrients and organic matter of faeces and the nutrients of urine that are diluted in the flushwater.Refers to (semi-solid) excrement that is not mixed with urine or water. Depending on diet, each person produces approximately 50–150 L per year of faecal matter of which about 80 % is water and the remaining solid fraction is mostly composed of organic material. Of the total essential plant nutrients excreted by the human body, faeces contain around 39 % of the phosphorus (P), 26 % of the potassium (K) and 12 % of the nitrogen (N). Faeces also contain the vast majority of the pathogens excreted by the body, as well as energy and carbon rich, fibrous material.Refer to biodegradable plant material (organic waste) that must be added to some technologies in order for them to function properly. Organic degradable material can include, but is not limited to, leaves, grass and food market waste. Although other products in this compendium contain organic matter, the term organics is used to refer to undigested plant material.The liquid produced by the body to rid itself of nitrogen in the form of urea and other waste products. In this context, the urine product refers to pure urine that is not mixed with faeces or water. Depending on diet, human urine collected from one person during one year (approx. 300 to 550 L) contains 2 to 4 kg of nitrogen. The urine of healthy individuals is sterile when it leaves the body but is often immediately contaminated by coming into contact with faeces.Describes technologies for on-site collection, storage, and sometimes (pre-) treatment of the products generated at the user interface. The treatment provided by these technologies is often a function of storage and is usually passive (i.e. requires no energy input), except a few emerging technologies where additives are needed. Thus, products that are ‘treated’ by these technologies often require subsequent treatment before use and/or disposal. In the technology overview graphic, this functional group is subdivided into the two subgroups: “Collection/Storage” and “(Pre-)Treatment”. This allows a further classification for each of the listed technologies with regard to their function: collection and storage, (pre-) treatment only or both.Describes the transport of products from one functional group to another. Although products may need to be transferred in various ways between functional groups, the longest, and most important gap is usually between the user interface or collection and storage/treatment and (semi-) centralised treatment. Therefore, for simplicity, conveyance only describes the technologies used to transport products between these two functional groups. In the technology overview graphic, the conveyance functional group is subdivided into the two subgroups: “Emptying and Transport” and “Intermediate Storage”. This allows for a more detailed classification of each of the listed conveyance technologies.Refers to the methods through which products are returned to the environment, either as useful resources or reduced-risk materials. Some products can also be cycled back into a system (e.g. by using treated greywater for flushing).A functional group is a grouping of technologies that have similar functions. The compendium proposes five different functional groups from which technologies can be chosen to build a sanitation system:
User interface (U), Collection and Storage/Treatment (S), Conveyance (C), (Semi-) Centralised Treatment (T), Use and/or Disposal (U).
A sanitation system is a multi-step process in which sanitation products such as human excreta and wastewater are managed from the point of generation to the point of use or ultimate disposal. It is a context-specific series of technologies and services for the management of these sanitation products, i.e. for their collection, containment, transport, treatment, transformation, use or disposal. A sanitation system comprises functional groups of technologies that can be selected according to context. By selecting technologies from each applicable functional group, considering the incoming and outgoing products, and the suitability of the technologies in a particular context, a logical, modular sanitation system can be designed. A sanitation system also includes the management and operation and maintenance (O & M) required to ensure that the system functions safely and sustainably. Any substance that is used for growth. Nitrogen (N), phosphorus (P) and potassium (K) are the main nutrients contained in agricultural fertilisers. N and P are also primarily responsible for the eutrophication of water bodies.
An organism or other agent that causes disease.The means of safely collecting and hygienically disposing of excreta and liquid
wastes for the protection of public health and the preservation of the quality of public water bodies and, more generally, of the environment.

Describes the conditions under which putrefaction and anaerobic digestion take place.
User interface used for urination and defecation. The organic molecule (NH2)2CO that is excreted in urine and that contains the nutrient nitrogen. Over time, urea breaks down into carbon dioxide and ammonium, which is readily used by organisms in soil. It can also be used for on-site faecal sludge treatment. See. S.18Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.

Operation and Maintenance

A pour flush toilet has no mechanical parts and is thus robust and rarely requires repair. Despite the fact that it is a water-based toilet, it should be cleaned regularly to maintain hygiene and prevent the build-up of stains. Cistern flush toilets require maintenance for the replacement or repair of some mechanical parts or fittings. Buttons, levers and the mechanisms inside the cistern are especially vulnerable. To reduce water requirements for flushing and to prevent clogging, dry cleansing materials, products used for menstrual hygiene and solid waste in general should not be flushed down the toilet. This may need to be addressed as part of hygiene promotion activities  X.12 and requires a solid waste management  X.8 scheme.

User interface used for urination and defecation.

Health and Safety

The Flush Toilet is a safe and comfortable solution provided it is kept clean. Anal cleansing material should be provided, and a handwashing station has to be in close proximity to the toilet.

User interface used for urination and defecation.

Costs

The cost of a Flush Toilet depends very much on the model chosen and additional costs for subsequent collection, conveyance, treatment and disposal technologies should be considered. Operating costs depend on the price of water. Cistern flush toilets are more expensive than pour flush toilets.

Describes the transport of products from one functional group to another. Although products may need to be transferred in various ways between functional groups, the longest, and most important gap is usually between the user interface or collection and storage/treatment and (semi-) centralised treatment. Therefore, for simplicity, conveyance only describes the technologies used to transport products between these two functional groups. In the technology overview graphic, the conveyance functional group is subdivided into the two subgroups: “Emptying and Transport” and “Intermediate Storage”. This allows for a more detailed classification of each of the listed conveyance technologies.A functional group is a grouping of technologies that have similar functions. The compendium proposes five different functional groups from which technologies can be chosen to build a sanitation system:
User interface (U), Collection and Storage/Treatment (S), Conveyance (C), (Semi-) Centralised Treatment (T), Use and/or Disposal (U).
A sanitation system is a multi-step process in which sanitation products such as human excreta and wastewater are managed from the point of generation to the point of use or ultimate disposal. It is a context-specific series of technologies and services for the management of these sanitation products, i.e. for their collection, containment, transport, treatment, transformation, use or disposal. A sanitation system comprises functional groups of technologies that can be selected according to context. By selecting technologies from each applicable functional group, considering the incoming and outgoing products, and the suitability of the technologies in a particular context, a logical, modular sanitation system can be designed. A sanitation system also includes the management and operation and maintenance (O & M) required to ensure that the system functions safely and sustainably. The means of safely collecting and hygienically disposing of excreta and liquid
wastes for the protection of public health and the preservation of the quality of public water bodies and, more generally, of the environment.

User interface used for urination and defecation. Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.

Social Considerations

The Flush Toilet prevents users from seeing or smelling the excreta of previous users. Thus, it is generally well accepted. Provided that the water seal is working well, there should be almost no odour and the toilet should be clean and comfortable to use. Flush Toilets should reflect local user preferences ( sitter vs. squatter, anal cleansing practices, direction etc.) and should account for the accessibility and safety of all users, including men, women, children, elderly and disabled people X.10.

Consists of urine and faeces that are not mixed with any flushwater. Excreta is relatively small in volume, but concentrated in both nutrients and pathogens. Depending on the characteristics of the faeces and the urine content, it can have a soft or runny consistency.Refers to (semi-solid) excrement that is not mixed with urine or water. Depending on diet, each person produces approximately 50–150 L per year of faecal matter of which about 80 % is water and the remaining solid fraction is mostly composed of organic material. Of the total essential plant nutrients excreted by the human body, faeces contain around 39 % of the phosphorus (P), 26 % of the potassium (K) and 12 % of the nitrogen (N). Faeces also contain the vast majority of the pathogens excreted by the body, as well as energy and carbon rich, fibrous material.The liquid produced by the body to rid itself of nitrogen in the form of urea and other waste products. In this context, the urine product refers to pure urine that is not mixed with faeces or water. Depending on diet, human urine collected from one person during one year (approx. 300 to 550 L) contains 2 to 4 kg of nitrogen. The urine of healthy individuals is sterile when it leaves the body but is often immediately contaminated by coming into contact with faeces.Any substance that is used for growth. Nitrogen (N), phosphorus (P) and potassium (K) are the main nutrients contained in agricultural fertilisers. N and P are also primarily responsible for the eutrophication of water bodies.
An organism or other agent that causes disease.A person who prefers to sit on the toilet.A person who prefers to squat over the toilet.
User interface used for urination and defecation. The organic molecule (NH2)2CO that is excreted in urine and that contains the nutrient nitrogen. Over time, urea breaks down into carbon dioxide and ammonium, which is readily used by organisms in soil. It can also be used for on-site faecal sludge treatment. See. S.18

Fact Sheet Overview

Input Products

Faeces
Flushwater
Urine

Output Products

Blackwater

Emergency Phase

Acute Response + +
Stabilisation + +
Recovery + +

Challenging Ground Conditions

Semi-Suitable

Application Level / Scale

Household + +

Water-based and Dry Technologies

Water-Based

Management Level

Household + +
Shared +
Public +

Technical Complexity

Space Required

Objectives & Key Features

• Barrier between user and excreta
• Flushwater needed
• Reduction of odour/flies

Strength & Weakness

  • The water seal effectively prevents odours
  • The excreta of one user are flushed away before the next user arrives
  • Suitable for all types of users (sitters, squatters, washers, wipers with toilet tissue)
  • Low capital costs; operating costs depend on the price of water
  • Requires a constant source of water (can be recycled water and/or collected rainwater)
  • Requires materials and skills for production that are not available everywhere
  • Coarse dry cleansing materials may clog the water seal

Selected References

Pour flush toilet drawings, dimensions and critical design criteria

Mara, D. D. (1985): Design of Pour-Flush Latrines. UNDP Interregional Project INT/81/047. The World Bank, Washington D.C., US

Mara, D. D. (1996): Low-Cost Urban Sanitation. Wiley, Chichester, UK

Maki, B. (2005): Assembling and Installing a New Toilet.

Vandervort, D (2007): Toilets: Installation and Repair.

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