Centralised drinking water systems serve millions of households around the world. However, these systems do often not reach the poorest or the most remote populations and quality and quantity of water provided are often unreliable due to poor operation and maintenance. Decentralised supply systems offer the possibility to provide safe drinking water where centralised supply systems are not feasible due to technical, economical or institutional reasons (e.g. in rural communities or informal settlements). Decentralised water supply refers to the small-scale purification and distribution of water. Decentralised treatment systems fall into three main categories: point-of-use systems (POU), point-of-entry systems (POE), and small-scale systems (SSS). POU and POE systems are designed for individual households while SSS can provide for community water supply, for emergency water supply in camps, or to purify water for sale in water kiosks. The choice of decentralised supply system depends on the local context and includes such factors as ease of use, maintenance needs, dependence on other utilities (e.g. electricity, fuel supply), and cost.
Centralised water supply is often considered the optimal water supply system, since it provides the most convenient service. However, in 2008, only 57% of the global population got its drinking water from a large-scale piped connection in the user’s dwelling, plot, or yard. In developing regions, this percentage was only 49%, with a large disparity between urban (73% having access) and rural communities (31% having access) (UNICEF WHO 2011).
Moreover, large distribution networks have high maintenance costs and are often prone to failures because of poor operation and maintenance. Failure of centralised systems to provide clean, adequate drinking water depends on a number of technical (see also intermittent supply and leakage control), economic, and legal factors. Because of the large amount of infrastructure (e.g. treatment plants, pipes, etc.) needed, there are many situations where it may not be possible to connect the whole population to the centralised supply system, such as in rural areas where populations are dispersed over large surface areas. Especially in developing or transition countries, high population growth in urban areas often leads to the establishment of informal settlements which remain disconnected from supply lines, as providing centralised supply is not technically or economically feasible. Moreover, as these settlements are frequently illegal, the government has no obligation to provide water and sanitation services. Furthermore, centralised water treatment and distribution facilities are often poorly maintained and fall into disrepair, so that even when users are connected to the centralised supply network, the quality and quantity of water may be unreliable (see also intermittent water distribution).
Decentralised supply offers the possibility to provide clean, reliable drinking water to rural or informal settlements where centralised systems are not economically or technically possible. Even when centralised drinking water is provided, decentralised supply can supplement other water uses in agriculture (e.g. precipitation water, optimised irrigation), or at home (see also optimisation of water use at home, rainwater harvesting rural for toilet flushing, optimised toilet systems, or water-saving appliances).
Decentralised supply systems are classified based on the quantity of water they can supply. There are three main categories of decentralised supply systems:
- Point-of-use (POU) supply: treats approximately 25 l/day for one household (see point-of-use water treatment).
- Point of entry (POE) supply: treats all water entering into a household, usually as an additional purification of water from a centralised supply.
- Small-scale systems (SSS): provides water to communities in quantities of 1,000-10,000 l/day. SSS are often also employed as emergency camp water supply systems (see water purification in emergencies).
Decentralised Water Sources
While surface water sources (e.g. lakes, rivers, man-made reservoirs, etc.) may be collected and purified, groundwater or rainwater are more favourable due to the lower risk of contamination with pathogens.
Decentralised Water Purification
Once a water source has been identified, it needs to be purified before being safe to consume. POU and POE systems use purification methods that can be divided into three main categories:
Heat or radiation
Using heat or radiation can effectively destroy pathogens. This includes techniques such as boiling, solar radiation, SODIS, and UV tubes. However, while pathogens may be killed, these methods have the disadvantage of providing no protection against recontamination.
Chemicals are widely used for purification and disinfection purposes. Methods include coagulation flocculation, precipitation (e.g. arsenic removal technologies), adsorption, ion exchange, and chemical disinfection (e.g. chlorination, WATASOL).
Physical removal processes
Physical removal processes separate contaminants from water using sedimentation or filtration techniques. Technologies include sedimentation or settling, filtration (e.g. membranes, ceramic and fibre filters, or colloidal silver filters), granular filter media (e.g. biosand filters, slow sand filtration, rapid sand filtration), or aeration.
The technologies employed in SSS are generally the same as in POU and POE systems, but scaled up to provide drinking water for communities in quantities of 1,000-10,000 l/day. They can also include technologies usually applied on a large scale: for example, liquid chlorine or chlorine oxide dosage may be replaced by chlorine tablets (see point of use chlorination and centralised chlorination) or coagulant flocculant mixing conducted in pipes. Slow sand filtration is often used for community water treatment in developing countries in combination with roughing filters, when maintenance or transport of chemicals is limited or not possible. SSS are also the systems most often employed to provide emergency water supply.
Where and when?
The suitability of a decentralised water supply and purification system depends on local needs and context. Before choosing a decentralised system, factors such as water quantity, water quality, and financial resources need to be closely regarded (see also decentralisation in water supply).
Whether used in a traditional way (e.g. boiling), introduced by NGOs or the market, point-of-use systems are currently widely applied by households with different financial resources in developing, transitional and sometimes even industrialised countries.
Point-of-entry systems are mostly used in industrialised countries as a supplementary treatment of tap or good quality well water, or in homes of wealthy people, hotels, childcare, and medical institutions of developing and transition countries.
The most typical application of small-scale systems is for community water supply. However, they have also had important applications in emergency water supply. Because emergency situations necessitate provision of clean water with limited time and resources, SSS are one of the best options to quickly provide safe water for community and camp water supply (see also POU water purification in emergencies).
SSS are also frequently employed to purify water for informal vendors selling water in water kiosks. This type of water supply can have the benefit of not only providing widespread clean water, but also for the kiosk attendants to earn commission from water sales. Learn more about water kiosks and informal vendors by reading about water vendors.
How to Optimise?
As previously mentioned, selection of an appropriate decentralised supply system depends on the local context. Generally, the following factors should be considered (see table below):
- Ease of use
- Maintenance needs
- Independence from utilities (e.g. electricity and fuel)
There are also ways to combine decentralised technologies with centralised supply systems if water quality from the centralised system is unreliable. This type of combined system is called a dual system, of which there are two main types:
- Dual central treatment: water of two different qualities is produced and distributed, one for drinking and one for general use (agriculture, washing, etc.).
- Central treatment for household purposes, decentralised treatment for drinking water quality.
Decentralised supply can lead to large improvements in public health by making water both available and safe to drink in areas where centralised supply fails to provide adequate, safe drinking water. However, regardless of the decentralised system used, safe storage of drinking water should always be practised in order to prevent recontamination.
The cost of decentralised supply depends on the technology chosen. While some can be prohibitively expensive, others are affordable even in poor communities. Smaller systems often require less operation and maintenance making them, in some contexts, more sustainable.
See the table below for more information about specific technologies.
Operation & Maintenance
Compared to centralised supply, decentralised supply requires time-consuming daily operation and maintenance for users. However, centralised water supply networks also require expensive, intensive maintenance, with the difference that it is out of the control of users. Therefore, decentralised supply has the benefit of putting users in control of their system maintenance. See the table below for more information about specific technologies.
Ease of use
Dependence on utilities
Depends on fuel availability
Depends on fuel price
Solar disinfection (POU)
+ (when low turbidity)
Regular, time consuming
UV lamps (POU)
+ (when low turbidity)
+ (training required)
Cleaning, annual replacement
Biosand filters (POU)
Once in a few months
Ceramic filters (POU)
+ (viruses unknown)
None, or tap pressure
+ (training required)
Regular, time consuming
Activated carbon filters (POU)
+ (if replaced)
Activated carbon filters (POE)
+ (if replaced)
+ (viruses unknown)
+ (viruses unknown)
Reverse osmosis (POU) (see advanced filters)
Tap pressure, electricity
Reverse osmosis (SSS) (see advanced filters)
Tap pressure, electricity
Bottled water (POU)
Depends on the region
Depends on the delivery distance
Bottled water (SSS): 50 m3/day
Depends on the region
Depends on delivery distance
POU water treatment systems can be used wherever centralised water supply is not available or not reliable for safe, adequate water. These include rural areas, where centralised water supply is unreliable, or informal settlements.
POE is suitable as a supplementary treatment for centralised water supply to ensure safety, and is usually implemented in industrialised countries or in the homes of wealthy families, hospitals, or childcare facilities in developing or transition countries.
SSS is suitable for community water supply in rural areas of industrialised, developing, or transition countries, and also to supply clean water for sale at water kiosks. SSS is the most common drinking water supply system in emergency situations to provide water in camps.
The specific technology that should be used depends on local contexts and should consider the water source, water quality, performance, ease of use, maintenance needs, dependence on utilities, and cost.
The report investigates access to and use of drinking water in greater detail than is possible in the regular JMP progress reports, and includes increased disaggregation of water service levels and analyses of trends across countries and regions. It focuses on the three key challenges of equity, safety and sustainability.UNICEF ; WHO (2011): New York and Geneva: United Nations Children's Fund (UNICEF) and World Health Organization (WHO) URL [Accessed: 05.03.2012]
This book provides a general introduction to a wide range of technologies. Among the topics covered are: planning and management of small water supplies, community water supplies in Central and Eastern European countries, water quality and quantity, integrated water resources management, artificial recharge, rainwater harvesting, spring water tapping, groundwater withdrawal, water lifting, surface water intake, water treatment, aeration, coagulation and flocculation, sedimentation, multi-stage filtration, desalination technology, disinfection, household level water treatment, technologies for arsenic and iron removal from ground water, and emergency and disaster water supply. Chapter 21: Water DistributionSMET, J. ; WIJK, C. van (2002): The Hague: International Water and Sanitation Centre (IRC) URL [Accessed: 29.02.2012]
This article describes the possibilities of decentralised water and wastewater systems in the U.S., particularly in urban areas.D’AMATO, V. ; MOELLER, J. ; STRIANO, E. ; (2011): (= Water Environment and Technology Magazine , 8 / 23 ). Water Environment Federation URL [Accessed: 25.10.2012]
International Market Survey on Membrane-Based Products for Decentralised Water Supply. POU and SSS Units
Small membrane-based systems stand as alternative solutions for rural areas and in developing and transition countries where a centralised treatment would not be affordable. Yet, in developing countries, membrane-based systems remain an expensive investment. Thus, simple, low-cost and long-term sustainable systems are required. In order to sustain a well-targeted development of small membrane-based systems, the current commercial offer of the international market should then be investigated. This is the concrete aim of this comprehensive survey.TECHNEAU (2008): TECHNEAU URL [Accessed: 26.10.2012]
This report has critically reviewed various HWT technologies on the basis of technical, social and economical factors and gives a good overview for an informed choice.WHO (2002): Geneva: World Health Organization (WHO) URL [Accessed: 26.02.2010]
This document is divided into three main parts. The first part contains an introduction to the topic and depicts some possible, simple techniques for treating water at the household level. The second part describes the possibility of collaborating to fight against waterborne diseases and the last part presents again some low-cost solutions.WHO (2007): The International Network to Promote Household Water Treatment and Safe Storage. Geneva: World Health Organisation (WHO) URL [Accessed: 11.10.2010]
This document describes the role of small-scale water supply in Europe. It provides a range of background information, case studies and lessons learned, and gives ideas for addressing issues relating to small-scale water supplies in national programmes. Additionally, information on further reading as well as current international networking activities with respect to small-scale water supplies is provided.WHO (2010): World Health Organization (WHO) URL [Accessed: 26.10.2012]
To improve access to safe water, particularly by the poor, developing country governments and the international development community are looking to the domestic private sector to play an expanded role. This report examines piped water schemes in rural areas of Bangladesh, Benin, and Cambodia and concludes that in the three study countries, un-served people could increasingly rely on service provision through the domestic private sector as the potential market the domestic private sector could be serving is very large.THE WORLD BANK ; WSP ; IFC (2013): (= Conference Edition ). Washington: The World Bank, Water and Sanitation Program (wsp), International Finance Corporation (IFC) URL [Accessed: 05.09.2013]
This Guide is an abbreviated compilation of the wide range of scientific, engineering, health and operational issues concerned with the control of lead in drinking water in small water supply systems. It explains why lead in drinking water may still be a threat to public health in small communities. It is aimed at Local Health Officials and the operators of drinking water supply systems that serve small communities. Its objectives are to raise awareness, to provide a basis for assessing the extent of problems, and to identify control options.HAYES, C. (2010): London: International Water Association (IWA) Publishing URL [Accessed: 01.11.2013]
Decentralised systems based on integrated urban water management (IUWM) and water sensitive urban design (WSUD) principles are being planned and implemented for urban developments, either as separate facilities or in combination with a centralised system. This report discusses identifying characteristics of decentralised systems in terms of technological options, features and scale. These characteristics were identified through analysis of cases studies in both SEQ and other regions of Australia.COOK, S. ; TJANDRAATMADJA, G. ; HO, A. ; SHARMA, A. ; (2009): (= Urban Water Security Research Alliance Technical Report , 12 ). Collingwood: Commonwealth Scientific and Industrial Research Organisation (CSIRO) URL [Accessed: 25.10.2012]
In Switzerland, rural communities have developed and managed their own water supply networks for a long time – in some cases over 100 years. This publication seeks to recount some experiences from the Swiss decentralised water supply approach that may be helpful or relevant. Even if the Swiss approach cannot be exported as it is, there still may be some lessons to be learned from more than a century of experience.SALADIN, M. ; (n.y): St. Gallen: Skat Foundation URL [Accessed: 26.10.2012]
Typically, the large urban areas represent concentrated demands, both due to large populations and large per capita use and waste. Most urban areas have depleted, polluted or destroyed their local sources of water like rivers, lakes and tanks and in many cases even groundwater. This case study presentsdecentralised approach where powers are devolved to local institutions and where co-ordination among the state, private sector and civil society are ensured for evolving water supply optionsSANDRP (1999): New Delhi: South Asia Network on Dams, Rivers and People (SANDRP) URL [Accessed: 30.10.2012]
One of the key problems facing the Kibera community is inadequate infrastructure compounded by lack of a clear policy framework and effective programs for meeting the needs of the residents of informal settlements. Poor water supply and sanitation are among the most serious infrastructural problems.WSP (1997): Nairobi: United Nations Development Programme (UNDP) Water and Sanitation Programme (WSP) URL [Accessed: 26.10.2012]
This training manual describes the need of safe drinking water and sanitation and provides relevant information on HWTS process, technologies. It is good reference material for trainers to conduct training on HWTS.CAWST (2009): Calgary: Centre for Affordable Water and Sanitation Technology (CAWST) URL [Accessed: 08.04.2010]
This PowerPoint presentation gives an overview of the governance of water supply in Kibera, one of the largest informal settlements in Africa, where only 16% of the population have access to water and sanitation facilities. Most people in Kibera obtain access to water from private and community-owned water kiosks.BILAL, S. ; (2011): Ottawa: International Development Research Centre (IDRC) Climate Change Adaption in Africa Project (CCAA) URL [Accessed: 26.10.2012]
This presentation outlines the benefits of decentralised water supply systems, the drivers and enablers in their adoption in Australia, a comparison between Australia and the US in implementing decentralised systems, and recommendations for Australia to move forward.MITCHELL, C. ; RETAMAL, M. ; FANE, S. ; WILLETS, J. ; DAVIS, C. ; (2008): Sydney: Institute for Sustainable Futures, University of Technology, Sydney URL [Accessed: 30.10.2012]