Storm Water and Sewage Network Management: Building Cities That Can Handle Water
A look at how cities are rethinking stormwater and sewage management—moving beyond bigger pipes toward smarter, integrated systems. Covers green infrastructure, real-time monitoring, and lessons from Singapore, London, Philadelphia, Copenhagen, and Tokyo on building water-resilient urban networks.
EDUCATIONALCASE STUDY
Rimashree
8/21/20266 min read
Stormwater and Sewage: Two Different Problems, One Connected System
Stormwater is rainwater that runs off roofs, roads, parking areas and other hard surfaces. Sewage, on the other hand, is wastewater generated by homes, offices, industries and commercial establishments.
Ideally, these two flows should be managed separately. But many older cities have combined sewer systems, where stormwater and sewage travel through the same pipes.
During normal rainfall, this can work reasonably well. During a major storm, however, the volume of water can suddenly become enormous.
When the network reaches its capacity, untreated mixtures of rainwater and sewage can overflow into rivers and other water bodies. These events are known as Combined Sewer Overflows (CSOs).
The result isn't just flooded streets. It can mean polluted waterways, environmental damage and serious public-health concerns.
That is why modern water management is shifting from simply building bigger pipes to creating smarter, more integrated networks.
When it rains heavily in a city, most people notice the same things: flooded roads, overflowing drains, traffic jams and waterlogged neighborhoods.
But beneath those streets, an enormous and largely invisible system is working to move millions of litres of water away from homes, businesses and public spaces.
That system is the stormwater and sewage network.
As cities grow, these networks are facing a difficult challenge. More buildings mean more wastewater. More concrete and asphalt mean less rainwater can soak naturally into the ground. And climate change is increasing the frequency and intensity of extreme rainfall in many parts of the world.
So the question is no longer simply, “How do we drain the water?”
It is becoming:
How do we manage water intelligently, before it becomes a flood, a pollution problem or a threat to public health?
What Does Effective Network Management Look Like?
A modern stormwater and sewage management system combines several layers of infrastructure and technology.
1. Strong Drainage Infrastructure
Traditional infrastructure still matters. Stormwater drains, sewers, pumping stations, detention tanks, canals and treatment facilities form the backbone of urban water management.
Regular inspection, desilting, cleaning and maintenance are equally important. A drainage network can have enormous capacity on paper, but a blocked inlet or sediment-filled drain can dramatically reduce its real-world performance.
Singapore, for example, manages around 8,000 km of drains, canals and rivers as part of its island-wide stormwater system. Its maintenance program includes drainage inspections, cleansing, structural repairs, monitoring and dredging where necessary.
2. Manage Rainwater Before It Enters the Sewer
One of the biggest ideas in modern stormwater management is simple:
Don't send every drop of rain into the drain immediately.
Instead, cities can temporarily store, absorb or slow down rainfall using:
Green roofs
Permeable pavements
Detention ponds
Bioswales
Tree trenches
Rainwater harvesting systems
Underground storage tanks
These systems reduce the sudden surge of water entering conventional drainage networks.
Singapore follows a Source–Pathway–Receptor approach. This means managing water where it falls, improving the pathways that carry it, and protecting areas where floodwater could eventually reach. New developments of 0.2 hectares or more are required to implement measures that reduce peak stormwater runoff.
It's a bit like controlling traffic before it reaches a highway rather than waiting for a massive traffic jam.
3. Bring Technology Into the Network
The next generation of water management is becoming increasingly data-driven.
Sensors, flow meters, pressure sensors, rainfall monitoring systems, remote telemetry, GIS and SCADA platforms can help utilities understand what is happening inside a network in near real time.
Instead of waiting for residents to report flooding, operators can monitor:
How much water is entering → where it is flowing → where capacity is becoming limited → where intervention is required.
This enables utilities to move towards predictive and proactive management rather than simply reacting after a problem occurs.
The U.S. Environmental Protection Agency specifically identifies smart data infrastructure, real-time notification and smart sewers, alongside green and grey infrastructure, as tools for managing combined sewer overflows.
Real-World Examples: How Cities Are Rethinking Water
Singapore: Managing Water at Every Stage
Singapore is one of the strongest examples of integrated stormwater management. Instead of relying exclusively on larger drains, PUB combines drainage upgrades with detention systems, green infrastructure, flood barriers, monitoring and maintenance.
Its Source–Pathway–Receptor strategy recognizes that flood resilience cannot depend on one piece of infrastructure alone.
The lesson is powerful:
A resilient city doesn't just move water faster. It manages water smarter.
London: The Thames Tideway Tunnel
London faced a different but closely related challenge: combined sewer overflows.
Heavy rainfall could cause sewage and stormwater to overflow into the River Thames.
The solution was the London Tideway Tunnel, often described as London's “super sewer.”
The completed system intercepts, stores and transfers sewage away from the River Thames for treatment. In May 2024, the main tunnel was connected to the Lee Tunnel, completing the network with a combined capacity of 1.6 million cubic metres.
It demonstrates how major underground infrastructure can protect a city's waterways while supporting long-term urban resilience.
Philadelphia: Turning Grey Infrastructure Green
Philadelphia has taken an especially interesting approach.
Through its Green City, Clean Waters program, the city has invested heavily in green infrastructure to reduce stormwater entering its combined sewer system.
Rain gardens, tree trenches, porous surfaces and other green systems help capture rainfall before it overwhelms underground pipes.
As of 2026, Philadelphia reports that the program has delivered thousands of green stormwater systems and prevented billions of gallons of polluted stormwater from reaching local waterways each year.
In other words, sometimes the best stormwater infrastructure isn't another giant concrete pipe.
Sometimes, it's a tree.
Copenhagen: Designing Streets for Extreme Rain
Copenhagen experienced a devastating cloudburst in 2011, causing billions of euros in damage.
The city responded with its Cloudburst Management Plan, combining conventional drainage improvements with parks, streets, retention areas and other surface solutions.
The plan proposed around 300 projects designed to retain, redirect or safely convey extreme rainfall. Some streets can function as temporary water pathways during extreme events, while parks and other public spaces can temporarily store water.
The concept changes the way we think about urban design:
A road doesn't always have to be only a road. A park doesn't always have to be only a park.
During a storm, public spaces can become part of the city's flood-management system.
Tokyo takes another approach.
The Metropolitan Outer Area Underground Discharge Channel is one of the world's largest flood-control infrastructure projects.
Completed in 2006, the system diverts floodwater from smaller rivers into massive underground tunnels before discharging it into the Edogawa River.
According to Tokyo Metropolitan Government information, the system has reduced the economic impact of flood damage by an estimated ¥148.4 billion during its first 18 years of operation.
It is a spectacular reminder that sometimes solving a city's water problem requires going beneath it.
The Future: From Drainage to Water Intelligence
The future of stormwater and sewage management will not be about one technology or one giant infrastructure project.
It will be about integration.
Sensors will provide real-time information. GIS will show where problems are occurring. SCADA systems will help operators monitor and control infrastructure. Smart pumps and valves can respond to changing conditions. Green infrastructure can reduce runoff at source, while underground networks handle what remains.
Melbourne's approach reflects this broader shift toward Integrated Water Management, bringing together stormwater, wastewater, drainage, water supply, treatment and reuse rather than treating each system as an isolated problem.
And that may be the most important change of all.
Building Cities That Work With Water
Water is not the enemy of a city.
Poorly managed water is.
A successful stormwater and sewage network should do more than prevent flooding. It should protect waterways, support public health, reduce pollution, improve resilience and, wherever possible, turn stormwater into a resource.
The world's leading cities are already showing what this can look like—from Singapore's source-pathway-receptor approach to London's Tideway Tunnel, Philadelphia's green infrastructure, Copenhagen's cloudburst planning and Tokyo's underground flood channels.
The lesson is clear:
The cities of tomorrow won't simply build bigger drainage networks. They'll build smarter water systems.
Because when the next extreme rainfall arrives, resilience won't be measured by how quickly a city can react.
It will be measured by how intelligently it was designed in the first place.
Photo by Tom Fisk
Photo by Imad Clicks
