C3.2 Recycling and reuse
Recycling and reuse is a useful planning and management tool at the river basin level. Urban effluent can be treated and returned to aquifers or rivers for dilution by natural flows and re-abstraction downstream (although there is a need to ensure the quality of returning effluent will not impose ecological or health risks). Treated effluent from industrial or municipal treatment plants may be piped directly for use in agriculture and horticulture (although the level of treatment should be adequate to minimise health risks, and recycled sewage only used for crops with low uptake of water/pathogens). Irrigation return water from drainage canals can be reused if mixed with fresh water. Water returned to rivers or used for groundwater recharge should be controlled in both quality and quantity by discharge permits or other regulatory tools (see C6) which take into account the needs of the aquatic environment and water available for dilution.
Recycling and reuse is feasible for individual water users in industry, institutions and large buildings, and at household level, to make the most of available water through recycling treatment processes. For instance, in water-short urban areas, water from rooftops or paved surfaces can be used for toilet flushing, sometimes with additional grey wastewater.
Recycling and reuse has wide applicability in general, but particular techniques or levels of recycling and reuse depend on local priorities and possibilities, and economic feasibility. It is most appropriate in areas where there are extreme water shortages, high water costs and high technical capabilities. High levels of technical management, monitoring and regulatory skills are needed for recycling and reuse to be both safe and effective. However, some less sophisticated techniques are being developed, such as guideline ratios for safe mixing of wastewater and fresh water, which can make this tool suitable for less developed areas. Also, low technology options of using grey water for irrigation are useful.
Use of recycling/reuse approaches can be stimulated through policy instruments (charges and tariffs which can increase the cost effectiveness of recycling and reuse, see C7.1), regulations and by-laws (C6.2) and incentive schemes to stimulate change. Regulations can be introduced to require changed industrial practice in water use. Awareness raising (C4.3) and the use of information and communication tools (C8) can stimulate recycling and reuse.