What are non-conventional water resources?
According to the FAO, the water scarcity affecting all continents – expected to intensify in the coming years as demands increase – the unevenness of water resource availability, and insufficient investment in specific infrastructure, are making the water sector look beyond conventional water resources and into other types of resources.
Non-conventional water resources refer primarily to recycled and desalinated water. Water can be used more than once, provided that, after is it used, it is returned to the environment with a quality that enables other uses afterwards.
In some cases, these resources represent an important alternative or, at least, a complement to meet the water needs in certain regions.
There is a range of terminology and definitions for water reuse globally, including water reuse, water recycling, and reclaimed water. The EU Regulation on minimum requirements for water reuse (2020/741) focuses on reclaimed water to be used for agriculture irrigation, and defines it as water as urban waste water that has been treated in compliance with the EU Urban Waste Water Treatment Directive (91/271/EEC) and which results from further treatment in a reclamation facility in accordance with a set of requirements. Those requirements are applicable to reclaimed water destined to be used for agricultural irrigation, and depend on the crop and the irrigation method. In Australia, water recycling is a generic term used for water reuse, defined as water taken from any waste (effluent) stream and treated to a level suitable for further use, where it is used safely and sustainably for beneficial purposes. The US EPA considers reclaimed water to be municipal wastewater treated to meet specific water quality criteria so it can be beneficially reused.
Together with desalination, water reuse or the recycling of reclaimed water that results from wastewater treatment, is one of the main non-conventional water resources, providing water for different uses. The main use is agricultural irrigation and, to a lesser extent, urban and industrial uses.
One of its main advantages is its reliability, since it is constant overtime, not dependent on climate or weather. In addition, it has a series of economic and environmental benefits. Nevertheless, wastewater reuse still faces limitations related to regulation and public reluctance due to health concerns.
In Europe, wastewater reuse falls under a regulatory framework established by the Water Framework Directive and the EU Regulation on minimum requirements for water reuse (2020/741).
Water desalination is the process of separating the salts from a saline solution to turn it into water that is suitable for human consumption, industrial or agricultural uses. Input water for desalination treatment may be seawater, saline or brackish groundwater coming from either coastal aquifers or aquifers isolated from the sea.
Although there are different methods to minimise the water salinity, such as distillation, nanofiltration or electrodialysis, reverse osmosis is the most widespread and advanced desalination technique in the world.
Its main advantage is that it comes from an almost endless source such as the sea and, in addition, it does not depend on climate or weather. However, it does have a series of disadvantages such as the high energy consumption associated with production, impacts on marine ecosystems or the high cost of the water produced.