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The reclamation of water from wastewater for drinking (potable) can be referred to as either direct or indirect potable reuse. While there may be some debate regarding the distinction between direct and indirect reuse, possible definitions for each approach are given below. These definitions have been summarised from the Australian Government Department of Health and Aged Care
Indirect Potable Reuse (Planned)
Indirect Potable Reuse can be defined as the reclamation and treatment of water from wastewater (usually sewage effluent) and the eventual returning of it into the current/natural water cycle well upstream of the drinking water treatment plant. Planned reuse indicates that there is an intent to reuse the water for potable use. The point of return could either be into a major water supply reservoir, a stream feeding a reservoir, or into a water supply aquifer (Managed Aquifer Recharge or MAR) where natural processes of filtration, and dilution of the water with natural flows aim to reduce any real or perceived risks associated with eventual potable reuse.
The practical distinction with potable reuse relates to temporal and spatial separation between wastewater treatment, the environment and consumption. Existing planned indirect reuse schemes (e.g. Water Factory 21 in Los Angeles, California) generally incorporate extensive separation to minimise health concerns and public opposition
Indirect Potable Reuse (Unplanned)
Unplanned (or Incidental) indirect potable reuse can be defined as wastewater entering the natural water system (creeks, rivers, lakes, aquifers), which is eventually extracted from the natural system for drinking water; with generally no awareness that the natural system contains treated wastewater.
Direct Potable Reuse
Direct Potable Reuse can be defined as either the injection of recycled water directly into the potable water supply distribution system downstream of the water treatment plant, or into the raw water supply immediately upstream of the water treatment plant. Injection could either be into a service reservoir or directly into a water pipeline. Therefore, the water used by consumers could be either undiluted, or slightly diluted recycled ater. In this definition, the key distinction with indirect potable reuse is that there is no temporal or spatial separation between the recycled water introduction and its distribution to consumers. Public perception of what extent of separation is required for reuse to become indirect may dictate the definition ultimately adopted