In the clamour of urban India’s rush toward development, a significant contributor to climate change is being ignored: its wastewater. A study conducted by Dr. R. Negi and Prof. M.K. Chandel at the Indian Institute of Technology Bombay, India, and published in Sustainable Cities and Society, examines the water-energy-greenhouse gas (WEG) nexus within India’s urban water systems (UWSs). The findings are useful and can contribute to India’s approach for net-zero emissions goal by 2070.
The invisible emissions from your tap
India’s rapid urbanisation demands a closer look at the infrastructure supporting its growth. Urban water systems, which include raw water extraction, treatment, distribution, and wastewater collection, are far more energy-intensive and emission-heavy than most assume.
The study adopts a comprehensive life-cycle approach to quantify both the embodied energy and associated greenhouse gas emissions across India’s UWS. Unlike traditional assessments that focus solely on electricity use, this method also accounts for the indirect energy used in infrastructure, chemicals, and background processes.
When only partial wastewater treatment is carried out (the more common scenario), total greenhouse gas emissions from urban water systems are significantly higher. Conversely, cities that collect and treat 100% of their wastewater (a less frequent scenario in India) show far lower overall emissions, even if treatment itself is energy-intensive.
The partial treatment paradox
At first glance, one might assume that full treatment of wastewater would lead to higher energy usage and emissions. But here lies the paradox. The study shows that partial treatment of wastewater in septic tanks leads to large-scale fugitive emissions (methane and nitrous oxide), which are far more potent than carbon dioxide. These gases often escape from untreated or improperly managed human waste, particularly in septic tanks and open drains.
The research makes a comparison: in scenarios where 100% of wastewater is collected and treated (CWT), the greenhouse gas emissions per cubic metre of water are lower compared to partial wastewater treatment (PWT). Even though treatment processes themselves consume energy, they significantly curb methane and nitrous oxide emissions from unmanaged waste. In other words, half measures are far more harmful.
Septic tanks
Septic tanks dominate India’s sanitation landscape, especially in peri-urban and rural-urban fringes. While promoted as low-cost solutions, they often operate as isolated systems without regular desludging or scientific maintenance.
The work reveals that these decentralised systems account for a disproportionately high share of emissions. The emissions from septic tanks, open defecation sites, and poorly managed on-site sanitation systems often go unaccounted in climate assessments.
The study emphasises that achieving net-zero must include urban water systems as a core component of climate policy. Currently, this sector is barely discussed in climate negotiations, yet its impact is undeniable.
Lessons from abroad
International comparisons from the study show that cities like Aveiro in Portugal and Cincinnati in the United States fare much better in terms of energy and emissions per cubic metre of water. Their advantage? Integrated, regulated systems that prioritise complete wastewater collection and treatment.
While these cities face their own challenges, their consistent monitoring, centralised treatment infrastructure, and use of renewable energy make them valuable case studies for Indian cities looking to reform their systems.
Another critical barrier is data. Lack of database about water and sanitation systems on public domain is one of the hurdles for sustainability assessment. Nevertheless, the study used process-based modelling and country specific emission factors, with robust uncertainty assessment to show the baseline sustainability status of a typical Indian urban water system.
A nationwide effort to map emissions from the urban water cycle would go a long way in creating evidence-based policies. Climate-smart sanitation begins with data-smart planning.
Why it matters, now more than ever
India’s urban water systems sit at the intersection of human health, environmental sustainability, and climate responsibility. Ignoring them is no longer an option.
With record-breaking heatwaves, extreme rainfall, and shifting monsoon patterns, climate change is no longer a distant threat for India. Water scarcity and quality issues are already affecting millions, and urban areas are becoming epicentres of both climate vulnerability and carbon emissions.
As the country builds smart cities and chases climate targets, the question is not whether India can afford to invest in wastewater infrastructure, but whether it can afford not to.
Wastewater is not just a hygiene issue. It is a climate issue. And the pipes below our feet may well hold the key to a cleaner, cooler, more sustainable India. What role do you think your city should play in tackling climate change?
Reference
Negi, R., & Chandel, M. K. (2022). Assessment on embodied energy and greenhouse gas emissions in urban water system from life cycle perspective: A typical case of India. Sustainable Cities and Society, 86, 104152. https://doi.org/10.1016/j.scs.2022.104152
