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Water reuse: Supplementary water

Manila : Water reuse is fast becoming an option in water scarce countries, but is accompanied by multiple issues. What key success factors should decision makers consider?

Recycling and the water cycle

We all know what happens in the Water Cycle; wastewater is actually recycled through an extensive and long natural treatment. Before water treatment technology, untreated wastewater is discharged into surface water, transported to the sea, evaporated, and finally comes back as rainfall to reload surface and underground waters. With high level water treatment technologies, water reuse is now a possibility for decision makers. In fact, treated water reuse has considerably shortened the Water Cycle .

Water reuse involves multiple and related technical, financial, economic, and social issues that need to be resolved before embarking on water reuse projects. Decision makers are now confronted with more options, since water reuse can now be considered as a water resource, and introduced, as such, in the water resources and water supply planning process.

Direct or indirect water reuse?

Treated wastewater can be reused directly for industrial process water, secondary water supply network, irrigation or spray irrigation, among others. Few, however, have been successful, mostly because of technical and financial constraints.

Direct reuse requires the doubling of the distribution network with dedicated "water reuse" pipes, which involves a large capital expenditure. In addition, pricing policy for water reuse, especially in a context of low water and wastewater tariffs, is very often not sustainable, and alternative self-supply, such as underground water, is usually preferred. Although water reuse point collection by trucks at the wastewater treatment plant is a good option for watering plants, high level of treatment combined with very effective disinfection are needed to prevent contamination. Direct water reuse in onsite sanitation systems in general and septic tanks in particular is not recommended, because of a high risk of contamination. Water reuse for irrigation, meanwhile, is highly dependent on water quality, most importantly on salinity.

Indirect water reuse, mostly through aquifer and surface water recharge, is gaining social acceptance and is the preferred manner to implement large scale water reuse plans. Water reuse is diluted with underground or surface water and benefits from an additional treatment during the water production process.

Key success factors for water reuse

Policy and decision makers should consider the following in planning, developing, and implementing water reuse programs and schemes:

Clear policy for pricing, planning, implementation, and regulation. Alternative water sources must be controlled to remove market-access barriers, and sustainable water and wastewater tariffs should be enforced with a sound pricing mechanism for water reuse. Unified water reuse quality and technology standards, based on applications/classifications for both direct and indirect usage are a pre-requisite. The selection of suitable technologies for sustainable water reuse production relies on adequate technical criteria and policy.

Clear marketing and communication plan to the population. In raising awareness on water reuse, the lack of water resources available and the reliability of water reuse in terms of quality should be adequately explained. A small scale water reuse demonstration project that can be visited by the public is one of the best ways to gain social acceptance.

Realistic assessment of the demand for water reuse. The demand may be affected by pricing, but is also driven by reliability and quality of the supply. Overdesign is a common problem. Maintenance and repair downtimes affect water reuse quantity and quality and should be taken into consideration during the design stage of the water reuse project to provide alternative sources of water, in case problems during the water reuse production process arises.

Realistic assessment of investment cost for additional tertiary treatment at the wastewater treatment plant and additional piping for water reuse delivery. Users’ requirements for different water quality need to be understood by both parties. It should be very clear who is paying for what: multi-sources investment and public-private partnerships are well adapted to finance water reuse projects.

Combination of water reuse production with point-of-sale distribution. The objective is to minimize additional piping requirement, which adds to the cost of the project and can therefore affect the project’s financial sustainability.

Operation and maintenance. Traditionally, a water reuse project is managed by the wastewater company. However, the water supply company, with its capacity and skills, may be better suited for managing high level treatment, pressure pipes, and customers.

Indirect water reuse is the preferred approach. In urban areas with limited water supply or stressed water resources however, direct water reuse can be suitable and sustainable. Provided there is a high standard treatment process in place, direct applications can include street cleaning, watering large gardens, and industrial cooling.

The future of water reuse

Water reuse as water resources or water supply is a new field and definitely an option for policy and decision makers. Comprehensive planning of water reuse should be systematically addressed in a Water Resources and Water Supply Master Plan, especially in an urban context.

With water reuse technology, cost, and mentality expected to change over time and with the impact of climate change on water resources already happening, water reuse planning, scope, and implementation will also evolve.

Hubert Jenny is senior urban development specialist at the Asian Development Bank (ADB.)

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