Functional Groups

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A functional group is a grouping of technologies that have similar functions. There are five different functional groups from which technologies can be chosen to build a system. The five functional groups are:


User Interface (Technologies U.1-U.6): Red


Collection and Storage/Treatment (Technologies S.1-S.12): Orange


Conveyance (Technologies C.1-C.7): Yellow


(Semi-) Centralized Treatment (Technologies PRE, T.1-T.17, POST): Green


Use and/or Disposal (Technologies D.1-D.13): Blue

Each functional group has a distinctive colour; technologies within a given functional group share the same colour code so that they are easily identifiable. Also, each technology within a functional group is assigned a reference code with a single letter and number; the letter corresponds to its functional group (e.g., U for User Interface) and the number, going from lowest to highest, indicates approximately how resource intensive (i.e., economic, material and human) the technology is compared to the other technologies within the group.

User Interface (U) describes the type of toilet, pedestal, pan, or urinal with which the user comes in contact; it is the way by which the user accesses the sanitation system. In many cases, the choice of User Interface will depend on the availability of water. Note that Greywater and Stormwater do not originate at the User Interface, but may be treated along with the products that originate from it.

Collection and Storage/Treatment (S) describes the ways of collecting, storing, and sometimes treating the products generated at the User Interface. The treatment provided by these technologies is often a function of storage and is usually passive (e.g., requiring no energy input). Thus, products that are ‘treated’ by these technologies often require subsequent treatment before Use and/or Disposal.

Conveyance (C) 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 between User Interface or Collection and Storage/Treatment and (Semi-) Centralized Treatment. Therefore, for the sake of simplicity, Conveyance only describes the technologies used to transport products between these functional groups.

(Semi-) Centralized Treatment (T) refers to treatment technologies that are generally appropriate for large user groups (i.e., neighbourhood to city level applications). The operation, maintenance, and energy requirements of technologies within this functional group are generally higher than for smaller- scale technologies at the S level. The technologies are divided into 2 groups: T.1-T.12 are primarily for the treatment of Blackwater, Brownwater, Greywater or Effluent, whereas T.13-T.17 are mainly for the treatment of Sludge. Technologies for pre-treatment and post-treatment are also described (technology information sheets PRE and POST).

Use and/or Disposal (D) refers to the methods by which products are ultimately returned to the environment, either as useful resources or reduced-risk materials. Furthermore, products can also be cycled back into a system (e.g., by using treated Greywater for flushing).


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The material on this page was adapted from:

Elizabeth Tilley, Lukas Ulrich, Christoph Lüthi, Philippe Reymond and Christian Zurbrügg (2014). Compendium of Sanitation Systems and Technologies, published by Sandec, the Department of Water and Sanitation in Developing Countries of Eawag, the Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.

The 2nd edition publication is available in English. French and Spanish are yet to come.