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 six functional groups are represented by colour-coded columns as follows: Source, Intake, Abstraction, Treatment, Distribution/Transport, Household Water Treatment and Safe Storage.
Before exploitation can begin, the water source must be identified. In the acute phase of an emergency, the chosen water source may not be ideal (such as in terms of water quality) but may still be chosen due to other advantages (such as proximity and/or accessibility). As the emergency stabilises, more time may become available for developing sustainable alternative sources (e.g. a Groundwater source [S.5] requiring less ongoing treatment or a Spring [S.6] amenable to gravity flow rather than pumping).
The intake chosen depends, for example, on the time available to build it, and thus in the acute response phase, the choice of intake is often limited to those that can be developed quickly, such as a River or Lake Intake [I.3], or where existing Wells [I.7] or Boreholes [I.8] can be commandeered. Again, as the emergency progresses, additional time availability may allow the construction of other intakes more suited to the ongoing situation.
The water will need to be abstracted from the intake via an energy source. During the acute phase of a response, this often means some kind of pump (see [A.1]–[A.9]) that is powered by Electricity [S.11] or Diesel [S.12], although these may be replaced with more sustainable alternatives over time, such as Gravity [S.7] or Solar Energy [S.10].
Following abstraction, the water will usually need treatment prior to distribution. The level and complexity of the required treatment largely depends on the water quality and the standards and indicators to be reached, though this is also dependent on the stage of the emergency response. For example, in the acute phase, the priority is always to reduce microbiological contamination immediately, as this has the highest short-term health impact. Over time, other treatment methods can be added to address additional sources of contamination that have long-term health impacts (e.g. fluoride). In the acute response, prefabricated, packaged water treatment plants are very useful, as they are designed to treat turbid or contaminated surface water in large volumes. They also tend to use treatment methods such as (Assisted) Sedimentation with or without Filtration ([T.4], [T.5]) that are effective reducing significant amounts of chemicals that may have long-term health impacts. Over time, more sustainable treatment options that take longer to set up can be designed. For example, Slow Sand Filters [T.9] dramatically reduce the chemical requirements in water treatment, thus reducing running costs.
Subsequently, treated water will need to be both transported from the source to the vicinity of the users (such as using trucks or pipes to transport water to storage tanks) and from the storage tanks to the users (such as using pipes and jerrycans). In the acute response, it is common to rely more on short-term solutions such as Water Trucking [D.3] to transport water to Flexible Bladder [D.5], which in turn are connected to Tap Stands (see [D.]). However, solutions like water trucking are very expensive and bladder tanks are not robust in the longer term. Hence other transport/distribution systems that are less expensive, more sustainable, and more convenient should be deployed as soon as possible. These include pipelines using gravity or solar pumping, tanks with larger volumes made from more robust materials (see [D.6]) and distribution systems that bring water closer to, or even into, the household (see [D.7], [D.8]).
Drinking water must be stored safely in the household, and users can perform additional treatments within the household if necessary. Historically, certain household-level water technologies have been useful in the acute response before centralised treatment is set up or where it is not possible, e.g. the use of Coagulant-Flocculant Sachets [H.8]. In some acute situations where the population is already familiar with a particular household water treatment product, these can be included as part of the first non-food item distributions in the acute phase to help address water quality, especially in dispersed populations. Overall, many of these household-level water treatment systems are also good long-term solutions where centralised water treatment is not reliable and where pilot interventions can be done prior to scaling up, potentially using local markets to do so.
Some humanitarian WASH organisations also use package systems consisting of several technologies from the functional groups presented above that are usually flown in, are immediately deployable and allow for a safe provision of water from the source to the user in a variety of contexts. These systems are usually only used in the acute response before context-specific, long-term solutions can be identified and set up or existing systems can be rehabilitated.
It is important to note that it is not always necessary for water to pass through all functional groups to reach a consumer. In some systems, treatment is excluded due to the high quality of the source water. Water can also be supplied by gravity to avoid the need for pumping.
There are multiple factors that influence an initial decision about which technologies to choose in an emergency. In reality, some experience is required to choose the most suitable technologies for the respective response phase, and it is not possible to be too prescriptive about this. The following steps provide some guidance to determine appropriate water supply technology options for specific contexts:
- Assessment of the initial situation (see [X.1] – [X.4]), including the identification and accessibility of available water sources with sufficient yields, the practices, preferences and water demand of the user groups to be served, the geographical conditions, the existing infrastructure and services in the area and the institutional and regulatory environment.
- Identification of technologies that may be appropriate for each of the functional groups based on the technology overview and the more detailed descriptions from the Technology Information Sheets. In the Treatment (T) functional group, multiple technologies may be applicable depending on potential contamination of the available water resource(s). Parts of a water supply system may already exist that can be integrated.
- Combine technologies logically to build several appropriate water supply systems.
- Compare the systems and iteratively change individual technologies based on considerations such as user/community priorities, time pressure
