Drinking water supply systems can be graphically presented as a sequence of functional groups that can be linked together in various combinations. All components of the system, from the source to consumption, form a part of this sequence and are considered and displayed. The functional groups cluster the technologies that have similar functions. The eCompendium proposes six different functional groups from which technologies can be chosen to build a water supply system or service (of which some may already be in place in a specific context that can potentially be rehabilitated). Each functional group is identified by a distinctive colour; technologies within a given functional group share the same colour code for easy identification. Also, each technology within a functional group is assigned a reference code with a single letter and number.
Source (S): refers to the original raw water source and considers whether it provides enough water as well as the energy sources needed to power abstraction, treatment and transportation of the water. Typically, groundwater or surface water resources are exploited, though in areas with sufficient rainfall, rainwater may also be an appropriate complimentary water source. The quantity, quality and location of the source determine the subsequent water treatment and water supply system design. A variety of energy sources is available ranging from gravity (if the water source is elevated) and human power (for abstraction of comparably small water volumes) to traditional (e.g. electricity or diesel) or renewable (e.g. wind and solar) energy sources.
Intake (I) refers to the withdrawal system that collects water from the source. For each water source, there may be one or more intake systems available. Some intake systems may act as a reservoir for storing water or provide a certain degree of treatment. Intakes can be classified according to the water source: rainwater, surface water or groundwater intakes. The choice of intake systems depends on a number of factors, including the volume of water needed for the target population, availability of appropriate surfaces, characteristics of the water body, flow and flow characteristics, hydrogeological conditions, water accessibility, availability and the risk of contamination. Properly constructed intake systems should provide convenient and efficient access to water sources as well as protect those sources from contamination and prevent harm to ecosystems.
Abstraction (A) refers to the various ways of extracting/abstracting water through a pump. Pumps can be divided into three broad categories, depending on how water moves through the pump: (1) impulse pumps, (2) positive displacement pumps or (3) velocity pumps. A wide variety of pump types are commercially available, each with specific operational advantages. Choosing the most appropriate water abstraction technology depends on a range factors, such as the water source, intake structure, available energy source, elevation, required capacity, O & M requirements, local availability of components and service, socio-cultural and environmental considerations and other infrastructure already in place.
Treatment (T) refers to technologies for water treatment, which are generally appropriate for a larger group of users, such as communities, semi-centralised applications in neighbourhoods, and more centralised applications in urban areas. Water treatment technologies can be divided into three groups: (1) pre-treatment with the main objective of reducing raw water turbidity, (2) targeting primarily microbial contaminants and (3) targeting chemical contaminants of various origins, including high salinity. Some technologies can function as a single-step treatment, while others may need to be applied as part of a multi-stage treatment system.
Distribution/Transport (D) refers to technologies for delivering water from the source, pumping station or water treatment plant to the user. These are either communal distribution systems with varying complexity, scale and types of connections or privately adopted solutions. Distribution/Transport also includes water storage technologies that can play a significant role within the distribution system as well as at the Intake (I) and during Treatment (T).
Household Water Treatment and Safe Storage (H) refers to household water treatment and safe storage technologies used as single-stage water treatment alternatives when centralised or community scale treatment is not available or the quality of produced water does not meet the applicable standards. Should contamination occur during transport between the point of abstraction/collection and the point of use, household water treatment is a viable option to remedy this and includes the safe storage of water within the household.
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