In the face of water scarcity, recycled water is a valuable resource which can be used in several human activities, including agriculture.

Over time, water has become a topic of great interest due to its great importance for life. With its overexploitation and increasing contamination, it is essential to find alternatives to ensure water conservation and availability in order to support the lives of future generations. Water recycling plays an important role in mitigating the effects of water scarcity. Such measures consist in recovering water from different sources in order to reuse it in our daily lives.

The water that is considered suitable for recycling comes from municipal wastewater, industrial processes, agricultural runoff or rainwater. Recycled water majorly results from domestic use effluents and from commercial activities, which depending on their treatment, can be suitable for human consumption or for other applications.

There are a wide variety of activities in which we can use recycled water for potable and non-potable uses, such as:

• Irrigation for agriculture and green areas such as parks or gardens.
• Supply municipal water.
• Water for industrial processes such as power plants, refineries, mills and factories.
• Indoor use such as the toilet tank.
• Dust control or cleaning on roads or constructions.
• Recreational lakes, fountains and decorative ponds.
• Environmental restoration such as streams and wetlands.

Recycled water is an important source for agriculture, currently the European Union through the water reuse regulation (WRR) defines the minimum requirements for recycled water, and its irrigation applications depending on the quality and type of irrigation.

The quality of recycled water  is based on the presence of some microorganisms such as Escherichia coli, Legionella spp., or intestinal nematodes, and other parameters such as BOD5, total solids, and turbidity, thus being divided into 4 categories:

• A: Water intended for all types of irrigation that can come into contact with the edible plant.
• B: water intended for all types of irrigation, but not being in direct contact with the edible part of the plant, which must be produced above the ground, it can also be used for processed crops and non-food crops used for livestock.
• C: Water intended only for drip irrigation, avoiding direct contact with the edible part of the plant, which must be produced above the ground. It can also be used in the activities mentioned above.
• D: water intended for all types of irrigation, but only for industrial and energy crops.

The reuse of water in these activities reduces the dependence on surface water, which is increasingly scarce, also minimizing the effect it has on groundwater and reducing the discharge of treated wastewater into rivers and oceans.