An analysis published on 9 October 2026 by The Policy Edge argues that India's urban water challenge is less about whether to build infrastructure than about choosing the right scale, with centralised sewage treatment plants exposed to network costs, capacity risk and underuse that are reshaping how cities should plan their next plants (The Policy Edge).
Key takeaways
- Indian cities have sewage treatment plants that are more than 20 years old yet receive less than 50 percent of the sewage they were designed to treat (The Policy Edge).
- Collection networks can account for 70–80 percent of total sewerage project costs, which changes the economics of plant siting (The Policy Edge).
- Effluent violation rates for 0.01 MLD plants are typically ten times those of plants exceeding 100 MLD (The Policy Edge).
- Decentralised treatment systems can be two to three times more costly than centralised systems for the same overall capacity (The Policy Edge).
- Water security debates outside India are also pointing to distributed systems with built-in redundancy rather than single large assets (New Security Beat).
What happened: a research-backed argument for a missing middle
The Policy Edge article, based on research published in Water Policy (Volume 25) as part of Shweta Lokhande's doctoral research at IIT Bombay, recasts the centralisation-versus-decentralisation question for Indian urban water as a scale question (The Policy Edge). Mumbai is used as the worked example: the city draws more than 3,220 million litres of water a day from outside its boundaries, making it one of the world's major urban centres dependent on cross-basin water transfers (The Policy Edge).
The article documents two engineering risks that follow from concentrating capacity. Leakage in Mumbai's distribution network is estimated at between 20 percent and more than 50 percent in some cases, which the authors frame as both an operating cost and a planning constraint (The Policy Edge). Heavy rainfall that inundated Mumbai's Bhandup water complex also disrupted water supply across the region, an example used to show that a system can be efficient under normal conditions while remaining exposed to disruption at a critical facility (The Policy Edge).
For wastewater, the analysis shifts attention away from the sewage treatment plant itself. Infrastructure planning often centres on the plant, the article says, but sewage first has to effectively reach it, and collection networks can account for 70–80 percent of total sewerage project costs (The Policy Edge). The economic question, in the authors' framing, is not only how cheaply wastewater can be treated at a plant but how far sewage should travel before it is treated (The Policy Edge).
Scale also governs how well infrastructure tracks urban growth. The article notes that many Indian cities have sewage treatment plants that are more than 20 years old yet receive less than 50 percent of the sewage they were designed to treat, illustrating the cost of locking capacity into a forecast that has not materialised (The Policy Edge). Modular systems, the authors write, allow capacity to be added in phases as demand emerges, rather than asking today's users to pay for capacity that may not be needed for years (The Policy Edge).
Modularity is not a free option. The article reports that effluent violation rates for plants of 0.01 MLD are typically ten times those of plants exceeding 100 MLD, and that decentralised treatment systems can be two to three times more costly than centralised systems for the same overall capacity (The Policy Edge). The conclusion the article draws is the need for a "missing middle": units large enough to retain operational and economic advantages, but sufficiently distributed to shorten networks, prevent a single failure from disrupting the whole system and allow capacity to be added progressively (The Policy Edge).
The same logic of avoiding concentration is being applied to water security in other regions. A 1 June 2026 commentary from New Security Beat argues that Gulf states should invest in "more decentralized and climate-resilient systems that are less vulnerable to single points of failure during crises or conflict," reflecting the same shift away from relying on a small number of large exposed facilities (New Security Beat).
Specification read: what this means for a buyer or operator
Restated in buyer units, 0.01 MLD is 10 m³ per day, typically enough to serve a small housing cluster, a hotel, a hospital block or an isolated institutional campus, while 100 MLD is 100,000 m³ per day, a class of plant serving roughly half a million to one million residents at typical Indian per-capita sewage contributions. The article does not report a single headline capacity for a project, so the relevant scale for any operator reading this piece is the gap between these two endpoints, where the article identifies the "missing middle" of mid-sized, distributed treatment (The Policy Edge). Plants in that bracket are commonly delivered as an Integrated Sewage Treatment train, running screening and grit removal through primary clarification, a biological stage such as MBBR, SBR, MBR or A2O, followed by tertiary filtration and disinfection, and where reuse is the goal, a polishing step to make the reclaimed water usable for toilet flushing, gardening or industrial cooling. The reported debate in The Policy Edge bears most directly on the collection and siting stage of this train, not on the reactor itself, because the article's central point is that the cost driver is the sewer line, not the tank (The Policy Edge). If your plant is in the few-MLD to mid-tens-of-MLD range, sits inside a Municipal network that is struggling to deliver design flow, or is being scoped for a campus where the existing trunk sewer is at capacity, this research is a signal to ask suppliers about phased capacity, modular biological stages and shorter infeed sewer runs, rather than committing to one large reactor (The Policy Edge). For broader context on the biological stage that this class of plant depends on, see HydropureWater's Best Technology to Remove COD BOD From Industrial Wastewater (2026 Buyer Guide), and for sites where contaminant removal rather than hydraulic scale is the binding constraint, the PFAS Removal Methods Comparison 2026: Industrial Options Tested piece sets out the relevant decisions.
FAQ
Why are Indian sewage treatment plants running at less than half their design capacity?
The Policy Edge reports that many Indian cities have sewage treatment plants more than 20 years old that receive less than 50 percent of the sewage they were designed to treat, with the article attributing this to forecasts of urban growth that have not materialised on schedule (The Policy Edge).
How much of a sewerage project's cost is the collection network, not the plant?
The Policy Edge reports that collection networks can account for 70 to 80 percent of total sewerage project costs, which is the figure the article uses to argue that reducing the distance sewage has to travel can outweigh the per-megalitre efficiency of a large plant (The Policy Edge).
Is a smaller wastewater plant always cheaper or better?
No. The Policy Edge reports that decentralised treatment systems can be two to three times more costly than centralised systems for the same overall capacity, and that effluent violation rates for 0.01 MLD plants are typically ten times those of plants exceeding 100 MLD, so the article recommends a mid-sized, distributed configuration rather than the smallest units (The Policy Edge).
What should a buyer ask a supplier if they want a plant that can be expanded later?
The article recommends modular systems that can be expanded in phases as demand emerges, with each phase designed to be operable on its own, so a buyer should ask vendors for a staged capacity plan, parallel-train biological reactors, and confirmation that the collection network, not just the treatment unit, has been sized for the final phase rather than the first (The Policy Edge).
