India’s rivers and lakes have long been the backbone of its civilisation — providing water, sustenance and shaping its cultural beliefs. However, rapid urbanisation, industrialisation, and population growth have led to severe pollution, threatening both ecosystems and human health. Major rivers like the Ganga, Yamuna and Brahmaputra, along with numerous lakes, are heavily contaminated by untreated sewage and industrial effluents.
In urban areas, centralised sewerage systems are designed to transport and treat wastewater, but in reality, a large portion of sewage including septic tank overflows never reaches treatment plants.
Instead, it flows into open drains, streams and lakes, further degrading water quality. India’s drains carry a mix of domestic sewage, industrial effluents and solid waste which makes wastewater management more complex.
The challenge is even greater during monsoons when overflowing drains worsen contamination which happens because of improper calculation of organic and hydraulic volume.
As per the inventory maintained by Central Pollution Control Board (CPCB), by 2021, the total generation of sewage is 72,368 million litres per day (MLD) but the actual treatment is of only 20,236 MLD which demonstrates a huge gap in the wastewater management.
To address this gap, Swachh Bharat Mission (SBM) 2.0 is promoting I&D based wastewater management, particularly in cities where sewer networks are inadequate or nonexistent. Integrating I&D systems with existing wastewater management approaches enhances treatment efficiency and curbs pollution by diverting untreated sewage to treatment plants, preventing contamination of natural water bodies and reducing non-point source pollution. Following key steps to be considered for successful implementation of an I&D project:
Mapping and Monitoring Drains – Identifying critical drain outfalls and assessing pollution loads.
Interception Structures – Constructing weirs or collection chambers to capture wastewater before it enters rivers.
Diversion Systems – Installing pipelines or channels to transport captured wastewater to treatment plants.
Treatment and Reuse – Ensuring wastewater is treated to acceptable standards and, where possible, reused for agriculture, industry, or landscaping.
Intercepting sewage before it reaches rivers or waterbodies could be an intermediate way to reduce pollution. Projects like Namami Gange have seen improved water quality in key river sections. This approach is an intermediate and immediate solution which can be quickly implementable. This serves the purpose where a centralised underground sewerage network is not feasible.
Additionally, I&D solutions are highly adaptable, fitting both small towns with basic systems and large cities with advanced treatment facilities. Beyond economic and logistical benefits, cleaner rivers support aquatic life, sustain fisheries, and enhance biodiversity.
Diverting wastewater also helps prevent waterborne diseases, improving overall public health.
While I&D offer many benefits, their implementation comes with some challenges. The biggest hurdle is improper planning and design as well as inadequate treatment infrastructure - many cities simply lack the capacity to treat diverted wastewater. In many cases, sewage treatment plants effectively treat wastewater, only to release it back into the same polluted channels, undermining the cost and effort of cleaning.
Financial constraints also pose a barrier, especially for smaller municipalities that may struggle to fund basic infrastructures.
Successful implementation requires strong coordination among government agencies, industries, and local communities, ensuring that all stakeholders work together toward a common goal. Additionally, regular maintenance is essential to keep the system functioning efficiently and prevent failures.
Shining examples
Ahmedabad’s Sabarmati Riverfront Development Project has significantly improved the river's water quality through the implementation of comprehensive interception and diversion structures. A key component of this initiative is the installation of interceptor sewers along both banks of the river, designed to capture sewage from 38 discharge points.
These interceptor lines collect untreated sewage and, with the aid of newly constructed pumping stations on the reclaimed riverbanks, redirect it to augmented sewage treatment plants located south of the Vasna Barrage. This system effectively prevents untreated municipal and industrial waste from entering the river, thereby enhancing its ecological health and water quality.
Also, the eight Lakes Restoration Project in Coimbatore is also noteworthy.
This initiative incorporated a multi-faceted approach using advanced screening systems, diversion channels, and natural wetlands to manage and treat wastewater before it reaches local water bodies. Advanced screening systems intercept large debris and particulate matter, ensuring that only finer pollutants enter the diversion channels.
These channels then redirect the water to treatment facilities or natural wetlands, where tertiary treatment processes take place.
Diversion channels ensure that treated water flows safely without overloading treatment plants, while natural wetlands serve as biofilters, utilising plants and microorganisms to further purify the water, removing excess nutrients and pollutants.
This combination revitalises local ecosystems, improving water quality and supporting biodiversity, as seen in projects around the Yamuna River, where such integrated methods have led to cleaner water and healthier habitats.
The Mahadevapura Lake interception and diversion (I&D) project employs hydraulic diversion structures to capture wastewater before it enters the lake, redirecting it to a 1 MLD Decentralized Wastewater Treatment System (DEWATS). The system includes screened intake structures to remove solid waste, followed by diversion channels and culverts that transport the wastewater to sedimentation and balancing tanks.
From there, the flow is regulated and processed through an Anaerobic Baffled Reactor (ABR) and Anaerobic Filter for organic load reduction. Planted Gravel Filters (PGFs) and floating wetlands provide tertiary treatment before the treated water is released back into the lake. Box culverts and silt basins at inlet points help manage hydraulic loads and prevent sedimentation, ensuring effective pollution control while supporting ecosystem restoration.
Interception and diversion project at Assi river, Varanasi
The Assi River interception and diversion (I&D) project in Varanasi utilises screening mechanisms, diversion channels, and interceptor pipelines to capture wastewater before it enters the river, redirecting it to treatment facilities.
Fifty MLD of sewage is diverted to the Ramana Sewage Treatment Plant (STP), while the remaining 30 MLD undergoes ozonation-based advanced oxidation treatment to break down pollutants. Interceptor drains and sedimentation structures regulate flow and prevent untreated discharges, while pilot bioremediation initiatives using bacterial cultures enhance organic matter degradation. These interventions ensure wastewater is treated effectively, reducing direct pollution into the Assi River and ultimately improving the Ganga's water quality.
The Namami Gange Program has made remarkable strides in pollution control through Interception & Diversion (I&D) projects, significantly improving water quality in key stretches of the Ganga. In Uttar Pradesh state, a total of 154 drains have been intercepted and diverted, reducing the direct discharge of untreated sewage into the river.
Notable projects include the Sisamau Nala interception in Kanpur, which diverts 140 MLD of sewage to treatment plants, and the Sultanpur I&D initiative, which includes the construction of a 7 MLD STP and the upgrade of an existing 5 MLD waste stabilisation pond into a 10 MLD aerated lagoon STP to treat wastewater from six drains.
Additionally, an I&D project in Dehradun is set to tap 117 drains carrying untreated wastewater that flows into the Ganga via the Song River between Haridwar and Rishikesh.
Building on these efforts, 2023-24 saw the inauguration of major I&D projects across multiple states. On March 1, 2023, the Prime Minister inaugurated three key projects in West Bengal, including STPs in Bally (40 MLD), Kamarhati & Baranagar (60 MLD), and Howrah (65 MLD).
Shortly after, on March 2, 2024, twelve projects worth Rs 2,189 crore were launched in Bihar, with major interventions in Patna, Bhagalpur, and Saran. The momentum continued on March 10, 2024, when I&D networks were integrated into sewage treatment projects in Prayagraj (72 MLD), Jaunpur (30 MLD), and Etawah (45 MLD), Uttar Pradesh.
Further strengthening the program, the Union Minister of Jal Shakti laid the foundation stone for a 220 MLD I&D project in Meerut on January 18, 2024, with an estimated cost of Rs 370 crore. These initiatives highlight the government's commitment to restoring the Ganga’s health through comprehensive wastewater management.
To fully harness the benefits of interception and diversion, India must take a comprehensive approach to wastewater management. Expanding treatment infrastructure is essential, requiring significant investment in modern, high-capacity plants across the country.
Technology can play a transformative role, with Artificial Intelligence (AI) and Geographic Information System (GIS) enabling real-time monitoring of drains and pollution levels. Collaboration between the public and private sectors is equally crucial industries should be encouraged to actively participate in wastewater management through incentives and partnerships.
Lastly, true progress depends on community engagement. Educating and involving local populations will ensure long-term success, fostering a collective responsibility for cleaner rivers and lakes.
Interception and diversion (I&D) of drains offer a scalable solution to reduce river and lake pollution in India by preventing untreated wastewater discharge. This approach enhances water quality and supports sustainable water management.
However, when drains carry industrial waste and contaminated runoff, treatment becomes complex, often leaving residues that limit safe reuse.
Overloaded plants may struggle to remove all pollutants, compromising water quality. Effective I&D requires stricter pollution control and advanced treatment to ensure safe and sustainable water reuse.