Wastewater reclamation is increasingly regarded as an alternative water source to mitigate water scarcity in China. However, expanding wastewater treatment capacity alone may not be enough to ease this scarcity, since wastewater supply, treatment facilities, and reuse demand are not always geographically aligned.

These findings were highlighted in a new study led by Prof. SHEN Lei from the Institute of Geographic Sciences and Natural Resources Research of the Chinese Academy of Sciences, which was published in Nature Water.

The team's findings emphasize the need to tailor wastewater treatment and reuse strategies to local conditions rather than simply expand centralized infrastructure.

The researchers first compiled a national inventory of 10,826 wastewater treatment plants, integrating datasets on wastewater generation, sewer networks, reclaimed-water demand, water scarcity, infrastructure costs, and multiple future socioeconomic scenarios based on Shared Socioeconomic Pathways.

Their goal was to assess the effectiveness and economic viability of China's centralized wastewater treatment systems in alleviating water scarcity.

They found that, under current conditions, only around 450 million people reside in areas where wastewater reuse can both recover costs and substantially alleviate local water stress. Economic viability is a challenge particularly in areas with small wastewater volumes and scattered settlements.

As part of their study, the researchers identified the economic-efficiency boundary for centralized wastewater treatment. They discovered that at current wastewater treatment fees, plants generally require a capacity of 6,800–49,700 m³ per day to break even. In many areas without wastewater treatment services, building centralized systems would require extensive sewer networks while offering limited economies of scale.

These findings point to the need for a more flexible approach to wastewater infrastructure planning. The researchers recommend site-specific planning, with centralized facilities where wastewater is concentrated, combined with decentralized treatment in dispersed settlements.

Modeling results show that this hybrid strategy could meet national wastewater treatment and reuse targets while reducing infrastructure costs by 25%–37% in comparison with a purely centralized strategy. Cost savings would mainly derive from avoiding the construction of long sewer networks in sparsely populated areas and uneconomical small centralized plants.

According to the researchers, the findings suggest that future wastewater infrastructure planning should shift from capacity-oriented expansion toward demand-driven system optimization, matching facility scale to local patterns of population distribution and wastewater generation.