Evaluating the global wastewater’s untapped irrigation potential

Wastewater has been increasingly considered an untapped resource rather than a waste. It can be used for water supply, aquifer recharge, energy generation, and fertilizer production, contributing concurrently to achieving multiple Sustainable Development Goals. Currently, treated wastewater is used for irrigation in different water-scarce countries like Israel and Spain. Recent estimates suggest that treated wastewater irrigates 6 million hectares (Mha) of cropland worldwide, with global potential for irrigating 31-42 Mha. Nevertheless, these estimates often do not account for environmental, social, and economic conditions that may limit this potential, including irrigated crops’ spatial distribution, water quality requirements, and water conveyance options.

Our study advanced a spatial-explicit analysis of four different technological scenarios and estimated the untapped potential of wastewater irrigation at a global, regional, and national scale. We found that utilizing treated wastewater for irrigation can satisfy up to 4% of the global irrigation demand. Considering only water-scarce regions, reduce this global potential to roughly 2%. However, intensification and expansion strategies or scenarios can increase this irrigation share. For example, in ten countries, delivering treated wastewater to croplands by canals adds over 5% to the share of treated wastewater relative to total irrigation demand. An increase of over 1% is evident in 30 countries, mainly in the Middle East, North Africa, and Western Europe.

Increased wastewater treatment capacity (i.e., expansion strategy) potentially increases the share of global irrigation demand satisfied with treated wastewater to 6% -12%. Some regions’ potential exceeds 20% of their irrigation demand, e.g., China and North America. An increase in potential wastewater irrigation becomes significant when considering expansion scenarios (e.g., increased capacities to treat the wastewater).

Considering the changes in different regions’ water scarcity, we find that the potential share of irrigation demand satisfied by treated wastewater is significantly increased in North America, the United Kingdom, Europe, and Western Asia. We conclude that irrigation with treated wastewater in these regions can be an important climate change adaptation measure. Besides, we show that intensifying and expanding wastewater reclamation systems can help manage droughts in regions with high drought risk, like the Italian Po and French Loire River basins.

By exploring expansion and intensification strategies to reclaim treated wastewater, this work establishes an essential step towards planning the global and regional pathways to utilize this untapped resource, abating current and future water scarcity risks.