New York City’s sewage travels through roughly 7,500 miles of sewer lines to 14 wastewater treatment facilities spread across all five boroughs. Together, these plants process about 1.3 billion gallons of wastewater every day. What happens to it from there depends on whether you’re talking about the liquid or the solid portion, and whether it’s a dry day or a rainy one.
How Sewage Moves Through the City
When you flush a toilet or run a sink in New York City, that water enters the sewer system and flows mostly by gravity toward one of the city’s 14 wastewater resource recovery facilities. Along the way, 95 pumping stations help push wastewater uphill or across flat stretches where gravity alone won’t do the job.
About 60% of the city uses a combined sewer system, meaning rainwater and sewage flow through the same pipes. The remaining 40% has separate systems, with dedicated pipes for stormwater and sewage. This distinction matters a lot during heavy rain, which we’ll get to shortly.
What Happens at the Treatment Plants
Once wastewater reaches a treatment facility, it goes through several stages of cleaning. First, large screens catch debris like wipes, plastic, and other objects that shouldn’t have been flushed. The water then moves into settling tanks, where heavier particles sink to the bottom as sludge and lighter materials like grease float to the surface for removal.
After that initial separation, the wastewater enters a biological treatment stage. Microorganisms break down organic material in the water, essentially eating the dissolved waste. The water is then settled again, disinfected to kill remaining pathogens, and released as treated effluent into surrounding waterways. The entire process takes several hours from start to finish.
Where the Treated Water Ends Up
The cleaned water, called effluent, is discharged into the rivers, creeks, and harbors surrounding New York City. Depending on which of the 14 plants processes the wastewater, the effluent flows into the East River, the Hudson River, Jamaica Bay, Newtown Creek, the Harlem River, or other local waterways. This treated water meets federal and state quality standards before it’s released, and it’s a major reason New York Harbor’s water quality has improved dramatically over the past several decades. Whales, dolphins, and seahorses have returned to waters that were essentially dead zones in the mid-20th century.
Where the Solid Waste Goes
The sludge that settles out during treatment, known as biosolids, follows a completely different path. Across New York State, about 68% of biosolids end up in landfills, making that the most common disposal method. Another 16% is incinerated at high temperatures, which reduces it to ash that then gets landfilled. The remaining 16% gets a second life through beneficial reuse: land application as a soil amendment on farms, composting into landscaping material, or heat-drying into fertilizer pellets.
Heat drying removes nearly all the water from biosolids (typically reaching over 90% solid content), and the resulting pellets can be applied directly to soil or blended with other materials. Some biosolids are also used for mine reclamation, helping restore land that was stripped during resource extraction. The exact destination varies by contract and market conditions, and NYC’s biosolids have at various times been shipped to facilities in other states.
The Overflow Problem on Rainy Days
The combined sewer system covering 60% of the city creates a well-known problem. On dry days, the pipes easily handle household sewage and route it to treatment plants. But during heavy rainstorms, rainwater flooding into those same pipes can overwhelm the system’s capacity. When that happens, a mix of stormwater and untreated sewage overflows directly into local waterways. These events are called combined sewer overflows, or CSOs, and they’re the single biggest water quality challenge the city faces.
The city is investing heavily to fix this. The Newtown Creek CSO Storage Tunnel, a massive underground tank designed to hold overflow until plants can process it, has a budget allocation of $2.9 billion in the current capital plan. The concept is straightforward: capture the overflow during a storm, store it temporarily, then send it to treatment plants once the rain stops and capacity frees up.
Green Infrastructure to Reduce the Load
Rather than just building bigger pipes and tanks, the city is also trying to keep rainwater out of the sewer system in the first place. The Department of Environmental Protection has installed thousands of green infrastructure features across the five boroughs, each designed to absorb or slow down stormwater before it reaches the sewers.
Rain gardens are small planted areas with engineered soil that soaks up runoff from sidewalks and streets. Stormwater greenstreets work on the same principle but are typically larger, built into roadway medians and curb extensions. Blue roofs use weirs at rooftop drains to temporarily pool rainwater and release it slowly rather than sending it all into the sewer at once. Below ground, subsurface detention systems use gravel beds and perforated pipes to store runoff underground until it can soak into the earth naturally.
The city is also investing $1.5 million over the next few years in stormwater resiliency mapping, which will help identify neighborhoods most vulnerable to flooding and prioritize where to build these systems next. Combined with nearly $500,000 in new flood sensor funding, the goal is to better predict and manage the surges that cause overflows.
The Scale of the System
Processing 1.3 billion gallons of wastewater daily for over 8 million residents (plus commuters and tourists) makes New York’s system one of the largest municipal wastewater operations on Earth. The Department of Environmental Protection’s wastewater treatment operations budget for fiscal year 2026 is roughly $588 million, employing over 8,000 people. That covers everything from maintaining aging pipes to running the biological treatment processes at all 14 plants around the clock.
For all its challenges, the system works remarkably well on most days. The vast majority of NYC’s sewage is fully treated before it reaches open water, and the city’s waterways are cleaner now than they’ve been in over a century. The ongoing problem is those rainy days when the combined system hits its limits, and that’s where the billions in new infrastructure spending are focused.