Water reuse tactic

By the Department of Water and Sanitation

South Africa has limited freshwater resources and has been defined as ‘water stressed’ by international standards.

The reuse of water in South Africa accounts for approximately 14% of total water use, and return flows account for a large part of water available for use from some of the important river systems. The National Water Resources Strategy (second edition) identified water reuse as one of several important strategies to balance water availability with water requirements in future, and the extent of water reuse in South Africa is very likely to increase substantially over time. There is an associated risk that water reuse is unplanned, unregulated and/or results in unintended or undesirable consequences.

The reuse of water is widely practiced in the world, both in developed and emerging economies. Many countries have developed water reuse policies and associated laws and regulations. Water reuse internationally contributes to reconciling the gap between water availability and water needs in such countries as the United States of America, Spain, Australia, Israel and China.

The reuse of water in South Africa accounts for approximately 14% of total water use.

Within the above context, this document provides a strategy for a considered approach to the implementation of water reuse projects that is consistent with the National Water Resource Strategy 2, as well as national water policy and legislation.

Defining water reuse

Water reuse can be direct or indirect, intentional or unintentional, planned or unplanned, local, regional or national in terms of location, scale, and significance. Water reuse may involve various kinds of treatment (or not) and the reclaimed water may be used for a variety of purposes. These different kinds of water reuse have different implications for a reuse strategy. It is therefore important to be precise in the use of terminology. Definitions of commonly used terms are given in Table 1.

DWS tableTable 1: Water reuse terminology.

Understanding reuse in the context of water supply

There are essentially three generic sources of ‘used’ water associated with different scales of water reuse:

  • At a micro-level, the water that has been used by a household, a business, an institution or industrial facility, a power station, a farm, or a mine. The key feature is that this used water is available at a specific and local geographic location. The quantity and quality of water available for reuse will depend on how it has been used and if there is any local (on-site) treatment or not.
  • At a community or facility level, where wastewater has been collected from a group of users (typically within a natural drainage basin), and typically through a sewer network. In this case, the used water is available at the discharge point of the treatment facility at a quality that is dependent on both the characteristics of the inflow to the treatment facility as well as the treatment technology used and its effectiveness (both in terms of design and operational performance).
  • At a river system level, where used water (treated and untreated) has been discharged (or found its way) back into the river system. In this case, the used water is blended with the ‘fresh’ water in the river system. The quality of the river water will depend on the quality and quantity of the return flows, the state of the receiving water body and its assimilative capacity, and the ratio of fresh water flows to return flows (the dilution effect). At a river system level, it is estimated that approximately 1 800 million m3 per annum of water flowing in our rivers is return flow — that is, used water — accounting for 14% of the total available water in South Africa. At the treatment facility level, South Africa has more than 1 000 municipal wastewater treatment works, discharging approximately 2 100 million m3 per annum of treated effluent, back to the river systems. At the ‘micro level’, the availability of South Africa’s water for reuse may be broadly categorised and aggregated into different industrial, mining, power generation, and agricultural sources. Mines, in addition to using freshwater and reusing water, may also ‘generate’ water. This occurs through the filling of mine cavities and the need to pump this water, or the natural decanting of this water where pumping does not take place. This water is referred to as mine decant or mine drainage. This water may be acidic, saline and may contain heavy metals. The mine water typically needs to be treated before it can be reused.

3.1.1 Water quality and security of supply

Water quality and security of supply

The cost of water is strongly related to the source of water, the required water quality, and the associated treatment requirements (for both supply and discharge.)

Where water quality requirements are relatively low or where wastewater discharge costs are high, the reuse of water is likely to be more attractive.

Water quality as it relates to public health is important in considering water reuse as a supply option. Any real or even perceived threat to public health would be a fatal flaw.

The reuse of water may increase the security of supply for specific users and may therefore be attractive in these cases, even where the cost exceeds alternative supplies. Note that it is not necessarily the case that increased water reuse increases the security of supply for an overall water supply system.

Understanding the need for water reuse

Key drivers affecting water reuse choices 

Five key considerations affect choices related to water reuse as an option for water supply and augmentation:

  • Water quality and security of supply
  • Water treatment technology
  • Cost relative to other water supply alternatives
  • Social and cultural perceptions
  • Environmental considerations.

Although these are likely to be inter-related in practice, it is useful to discuss each in turn.

We will continue with each consideration in the next issue of Plumbing Africa. To obtain a full copy of the document, visit www.dwa.gov.za and search for ‘NWRS 2’.

Water re use

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