The research, led by Manimuthu Sathaiah of SRM Institute of Science and Technology’s College of Agricultural Sciences, together with colleagues from Tamil Nadu Agricultural University and other institutions, compared 240 coconut farms across Tamil Nadu. Half of these farms—120 in total—were irrigated with treated industrial effluent, while the other 120 served as conventionally managed control farms using standard water sources. Coconut was chosen deliberately: it is one of Tamil Nadu’s most economically important perennial crops, and its farmers have increasingly turned to alternative water sources as groundwater tables fall and surface supplies become unreliable. The researchers collected detailed primary data from all 240 farms, allowing a direct, field-based comparison rather than a modeled or hypothetical assessment.

What sets this study apart from earlier work on wastewater irrigation is its methodological breadth. Previous assessments of effluent reuse have typically stopped at farm-level profitability, asking only whether farmers earn more money from their harvests. Sathaiah and his colleagues instead deployed a social cost–benefit analysis, a framework rooted in classical welfare economics going back to A.C. Pigou’s foundational work on the economics of welfare. Under this approach, the true value of a policy or practice is measured by its effect on society as a whole—including people who never visit a farm but who benefit from cheaper coconuts, cleaner rivers, or new jobs. The framework also demands that external costs, such as health impacts on exposed workers and communities, be counted against the benefits rather than ignored.

The accounting produced a strikingly detailed ledger. On the benefit side, treated industrial effluent irrigation generated an incremental private economic benefit of ₹20,343.26 per hectare, reflecting higher yields and lower input costs on the effluent-irrigated farms relative to the controls. Treated effluents often carry nutrients such as nitrogen, phosphorus, and potassium, which can partially substitute for synthetic fertilizers, and the guaranteed availability of irrigation water in a scarce region allows farmers to maintain yields through dry periods that would otherwise stress their trees. To this private gain the researchers added a non-market benefit of ₹3,813.46 per hectare, estimated using the Contingent Valuation Method—a survey-based technique in which individuals express their willingness to pay for outcomes they value, such as improved environmental quality, even when those outcomes are not traded in any market.

A third component, the regional socio-economic benefit of ₹10,850.00 per hectare, captured the wider ripple effects of effluent-irrigated farming, particularly employment generation. Perennial tree crops like coconut are labor-intensive across the year, and farms with reliable irrigation sustain more consistent rural employment than those exposed to water uncertainty. Summing these three streams, the study found a total social benefit of ₹35,006.72 per hectare from treated industrial effluent reuse.

Against these benefits, the researchers set the costs that society bears from the practice. These measurable external costs came to ₹15,316.10 per hectare, comprising health impacts associated with exposure to the effluent and the expenses of soil reclamation where prolonged irrigation with treated wastewater degrades soil quality. Even industrial effluent that has passed through treatment is not pure water; it can carry residual salts, heavy metals, and organic micro-contaminants that accumulate in soils and pose occupational health risks to farm workers who handle it daily. By explicitly pricing these harms rather than treating them as vague caveats, the study provides an unusually honest assessment. Subtracting the external costs from total benefits yields the headline net social benefit of ₹19,690.62 per hectare.

Expressed as a ratio, the study found a social benefit–cost ratio of 2.29:1—meaning that for every rupee of social cost incurred by reusing treated industrial effluent, society gains roughly two rupees and twenty-nine paise in return. That figure is robust by the standards of public investment appraisal, where ratios above one generally justify proceeding and ratios above two are considered strongly favorable. Importantly, the researchers stress-tested their conclusion through sensitivity analysis, varying the assumptions about external costs and benefits across plausible ranges. The favorable welfare outcome held under all reasonable scenarios, suggesting the conclusion does not hinge on any single fragile estimate.

The timing of the research is significant. Globally, agriculture consumes roughly 70 percent of freshwater withdrawals, and competition among cities, industry, and farms is intensifying as populations grow and climate change disrupts rainfall patterns. India is among the most water-stressed large economies, with many of its industrial clusters located in the same arid and semi-arid regions as productive agriculture. Conventional responses—desalination, inter-basin transfers, and deeper groundwater pumping—are expensive, energy-intensive, or environmentally destructive. Reusing treated wastewater, by contrast, embodies the circular economy ideal: a waste stream from one sector becomes an input for another, simultaneously reducing pollution discharge into rivers and relieving pressure on scarce freshwater. International bodies including the Food and Agriculture Organization and the United Nations Environment Programme have highlighted wastewater reuse as a key adaptation strategy, and countries such as Israel, Australia, Spain, and Tunisia have built substantial reuse programs.

Yet the economics of reuse have remained contested. Studies from Spain, Chile, and elsewhere have questioned whether the costs of treating, transporting, and safely managing reclaimed water outweigh its benefits, particularly where farmers must pay market prices for the treated effluent. Others have documented genuine risks: the uptake of pharmaceutical residues and emerging contaminants by crops, impacts on soil microbial communities, and long-term salinization. Most previous cost–benefit analyses have also focused on municipal wastewater rather than industrial effluent, which typically contains a different and more challenging contaminant profile. By focusing on industrial effluent specifically—and by measuring both benefits and costs in the same welfare framework—the Tamil Nadu study addresses a genuine gap in the literature.

The study’s findings carry clear policy implications for India. If treated industrial effluent irrigation produces large net social benefits, then regulations and incentives that encourage safe reuse—rather than simply mandating discharge limits—could capture value that is currently being lost. The framework developed by Sathaiah and colleagues also gives policymakers a template for evaluating specific reuse schemes on their merits, weighing private farm gains, community willingness to pay, and employment effects against the health and soil costs that must be managed through proper treatment and monitoring. The sensitivity analysis suggests policymakers have some margin: the welfare case remains positive even if external costs are somewhat higher than estimated, provided treatment standards are maintained.

The authors are candid about the limitations of their work. Long-term environmental externalities—such as the multi-decade accumulation of heavy metals in soils, effects on groundwater beneath irrigated fields, and ecosystem impacts downstream—could not be monetized because of data limitations. Coconut is a deep-rooted perennial, which may buffer it against some contaminant uptake compared with leafy vegetables, and the health and soil reclamation costs captured in the study represent only the measurable portion of the practice’s full environmental footprint. Extending the welfare framework to other crops, other states, and longer time horizons remains a task for future research. The authors note that no datasets beyond those described were generated or analysed in the study, and the work received no dedicated funding.

Even with these caveats, the study offers a rare piece of good news in the often grim literature on water scarcity. It suggests that in at least one major agricultural economy, the conflict between industrial development and farming over water can be partially dissolved by engineering and economics working together: treat the effluent properly, monitor the soils, protect the workers—and the same water that once threatened rivers can sustain a coconut grove for decades. As one hectare after another in Tamil Nadu demonstrates, wastewater, handled with care, can genuinely become wealth.