Most cities in the United States get their water from surface sources like rivers, lakes, and reservoirs. A smaller number rely on underground aquifers, and a growing handful supplement their supply with desalinated seawater or recycled wastewater. The exact mix depends on geography, climate, and how much the city has grown beyond what local sources can provide.
Surface Water: The Most Common Source
Rivers, lakes, and reservoirs supply the majority of municipal water in the U.S. Cities build intake structures along these bodies of water to divert a controlled amount into their treatment systems. A typical river intake includes a diversion structure that maintains water at the right level, flow controls like sluice boards or sliding metal gates, and screens to keep out debris. From there, water flows through tunnels or canals to a treatment plant, often aided by gravity.
Reservoirs work a bit differently. Many were purpose-built by damming rivers, creating massive storage that buffers a city against seasonal dry spells. Water can be released from the reservoir through bottom valves, outlet sluices, or siphons placed over the dam. The key advantage of reservoirs is reliability: they hold water during wet months so cities can draw from them year-round.
Groundwater and Wells
Cities that sit above productive aquifers can pump water from underground. Groundwater is naturally filtered as it passes through layers of rock and sediment, so it often requires less treatment than surface water. Smaller cities and suburbs are more likely to depend on wells, but even large metros tap into groundwater as part of their supply. Los Angeles, for example, has historically drawn about 12 to 15 percent of its water from local groundwater basins.
The challenge with groundwater is that aquifers recharge slowly. When cities pump faster than rain and snowmelt can replenish the supply, water tables drop, wells go dry, and in some cases the ground itself compacts and sinks permanently. This is already happening in parts of California’s Central Valley and in the suburbs of Phoenix.
How New York City Does It
New York City’s system is one of the largest and most elegant in the world. It draws about 90 percent of its water from the Catskill-Delaware watershed, a network of reservoirs fed by rain and snowmelt in the Catskill Mountains. Three major reservoirs on the Delaware River’s headwaters, Rondout, Neversink, and Pepacton, feed into the Delaware Aqueduct, which carries water across the Hudson River and into the city’s distribution network.
The water travels roughly 125 miles, and most of that journey happens by gravity alone, with pumping needed for only about 45 percent of the route. Because the watershed is protected by strict land-use regulations, New York is one of the few large American cities that doesn’t need to filter its surface water. It’s treated with disinfectants and UV light, but skips the full filtration process that most cities require.
How Los Angeles Does It
Los Angeles sits in a semi-arid basin and has never had enough local water for a city its size. Historically, it solved that problem by reaching far away. The Los Angeles Aqueduct, completed in 1913, carries snowmelt from the eastern Sierra Nevada across more than 200 miles of desert. For decades, this single source provided over 75 percent of the city’s supply.
That share has been shrinking. Environmental regulations and drought have reduced flows from the Sierra, and the city now buys a growing portion from the Metropolitan Water District, which imports water from Northern California through the State Water Project and from the Colorado River. Projections show the aqueduct supplying about 40 percent of the city’s needs in the coming years, with MWD purchases rising to around 38 percent. Groundwater and a rapidly expanding recycled water program fill in the rest.
How Chicago Does It
Chicago’s situation is simpler than most major cities, because it sits beside one of the largest freshwater lakes on Earth. The city’s water begins its journey at intake structures called “cribs,” positioned about two miles offshore in Lake Michigan. Drawing water from that distance avoids the pollution and sediment that concentrate near the shoreline.
From the cribs, water flows through tunnels 20 feet in diameter to the James W. Jardine Water Purification Plant, located just north of Navy Pier. Jardine is the largest water treatment plant in the world. After treatment, Chicago’s system doesn’t just serve the city itself. It sells treated Lake Michigan water to more than 100 surrounding suburbs.
Desalination and Recycled Water
For coastal cities running low on freshwater, desalination turns seawater into drinking water by forcing it through membranes that strip out salt and other dissolved solids. The technology works, but it’s expensive. Producing one acre-foot of desalinated seawater (enough to supply roughly two households for a year) costs between $800 and $1,400, several times more than drawing from a river or reservoir. It also uses significant energy, which is why desalination remains a supplement rather than a primary source in most places.
Water recycling is gaining ground faster. In a direct potable reuse system, treated wastewater is purified through multiple advanced steps and returned to the drinking water supply. This was once considered unthinkable, but the technology now produces water that exceeds federal quality standards. Several states are developing regulatory frameworks for direct potable reuse, and cities across the American Southwest view it as essential to their long-term water security.
What Happens Before It Reaches Your Tap
Regardless of the source, municipal water passes through a treatment plant before it enters the distribution system. The basic steps are consistent across most cities: coagulation and flocculation (chemicals cause particles to clump together), sedimentation (those clumps settle out), filtration (water passes through layers of sand, gravel, or activated carbon), and disinfection (chlorine, chloramine, or UV light kills remaining bacteria and viruses).
The EPA sets legal limits on over 90 contaminants in drinking water under the Safe Drinking Water Act. Individual states can enforce stricter standards, but they can’t go below the federal baseline. Public water utilities test regularly and publish annual water quality reports that anyone can request or find online.
Aging Pipes and the Infrastructure Gap
Getting water from a lake or reservoir to a treatment plant is only half the system. The other half is the network of underground pipes that delivers treated water to homes and businesses. In many American cities, those pipes are decades old, and some date back more than a century.
The American Society of Civil Engineers gave U.S. drinking water infrastructure a C-minus in its 2025 report card, unchanged from 2021. The report specifically cited inadequate funding from state revolving funds, the primary federal mechanism for financing water system upgrades. Aging pipes lead to water main breaks, pressure drops, and in the worst cases, contamination from corroded lead or iron lines. The overall grade for American infrastructure was a C, and water categories scored below that average across the board, with stormwater systems receiving a D and wastewater a D-plus.
For most people, the water coming out of the tap is safe and reliable. But the systems delivering it are under growing strain from age, population growth, and climate shifts that are making traditional sources less predictable. Where your city gets its water today may not be where it gets its water in 20 years.