Economic and comparative quantification of waste reuse and desalination for urban uses

Abstract

Sustainable water management in urban environments requires exploring alternatives that reduce pressure on conventional water resources. Among other options, this study analyzes the technical and economic feasibility of wastewater reuse versus reverse osmosis desalination for urban water supply in coastal cities, using Spanish cases such as Madrid, Barcelona, Seville, and Bilbao as a reference. In areas such as the Cantabrian coast, traditionally well-supplied, resource pressure and climate change raise the need for resilient alternatives for water supply.
Reuse requires adding advanced tertiary treatment to existing WWTPs. Total costs (investment and operation) are estimated at €0.780/m³, also considering the need to build a secondary distribution network for non-potable uses, which represents a structural limitation. The main operating costs of regeneration are related to energy, reagents, waste management, and maintenance, while investment costs in transport networks represent a considerable burden. This option is economically advantageous compared to desalination, especially where existing infrastructure exists and the climate favors a significant demand for reused water.
Reverse osmosis desalination, on the other hand, has higher costs, with an estimated total cost of €1,271/m³. However, its main advantage is that the water produced is suitable for human consumption and can be directly integrated into the main water supply network without the need for additional secondary networks. This makes it a more robust option in contexts where increased resilience to droughts or meeting drinking water demands are required. However, its higher energy consumption and operating costs make it less economically competitive compared to reuse, except in cases where urban or climatic characteristics make the latter difficult to implement.
The study concludes that the most appropriate option depends on the local context and allows decision-making to be guided toward context-adapted solutions based on both technical and economic criteria.