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Chartered Institution of Water and
Environmental Management (CIWEM)

106-109 Saffron Hill, London, EC1N 8QS  
Tel: 020 7831 3110 Fax: 020 7405 4967
 

Direct and Indirect potable reuse

Direct potable reuse (i.e. treated wastewater directly reused for drinking water) is very rare because of the increased potential risk to public health and the negative public perception. Even though the technology is well proven, direct potable reuse is only justifiable when there is no other option for example in the desert or outer space. Currently the only place where direct potable reuse takes place on a municipal scale is in Windhoek, Namibia where treated wastewater combined with surface runoff is treated to provide potable water. Direct reuse is common practice for non potable applications in industry and irrigation.

Indirect potable reuse can be planned or unplanned. Conventional water treatment in many countries involves unplanned indirect potable reuse of treated wastewater. That is, water abstracted from rivers to provide drinking water includes treated wastewater that has been discharged upstream. It is unplanned in the sense that it is not an intentional part of the wastewater discharge policy that the water will be reused downstream for potable water supply. The abstracted water will still need to meet potable water standards if it is to suply drinking water. River water may go through several abstraction-treatment-use-treatment-discharge cycles before reaching the sea (see Figure 1). The pursuit of economies of scale has led to a tendency for large down-catchment wastewater treatment plants. Planned use by relocating treatment and shortening the use-reuse cylce could increase water availability for both environmental and other purposes.

Figure 1. Indirect Water Reuse

Indirect Reuse Diag

Health

The reason that indirect water reuse is not considered to pose a health risk is that that the treated wastewater benefits from natural treatment from storage in surface water and aquifers and is diluted with 'ordinary' river/ground water before abstraction to ensure good drinking water quality (part of a multi barrier approach in the water safety plan). The storage time provides a valuable buffer to measure and control quality. Direct potable reuse, however, is almost a closed loop system with limited storage and a shorter buffer time therefore increasing the risk.

 

Case Studies

Read about planned indirect potable water reuse in Germany and Singapore.

 

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Chartered Institution of Water and
Environmental Management (CIWEM)

106-109 Saffron Hill, London, EC1N 8QS  
Tel: 020 7831 3110 Fax: 020 7405 4967

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