New Jersey draws its water supply from a managed network that balances surface water and groundwater resources. As the most densely populated state, maintaining a reliable source for its nearly nine million residents requires a complex system of rivers, reservoirs, and deep underground aquifers. The state’s infrastructure is designed to capture, store, and distribute water across varied geographic regions, relying on both natural flows and engineered storage capacity. This dual reliance ensures that public water systems, private wells, agriculture, and industry have access to the necessary volume of fresh water.
Surface Water Systems
Approximately 74% of New Jersey’s total water withdrawal comes from surface water sources like rivers and reservoirs. These sources are the primary supply for the state’s densely populated northern and central counties. The Delaware River Basin is the largest single source, providing a significant volume of water managed and distributed through interstate agreements.
The Raritan River Basin is another major inland waterway contributing substantially to the surface water network. To manage the variable flow of these rivers, large reservoir systems were constructed to store water during wet periods for use during droughts. The largest storage facilities include the Round Valley, Spruce Run, and Wanaque Reservoirs.
These reservoirs are engineered to ensure a consistent volume of water known as a safe yield. This safe yield is the volume of water the system can routinely supply even during severe drought conditions. The Wanaque Reservoir is located in the north, while the Spruce Run and Round Valley Reservoirs are part of the Raritan Basin Water Supply System. The Delaware and Raritan (D&R) Canal also functions as a major conveyance system, transferring water from the Delaware River to central New Jersey.
Groundwater Reliance
While surface water serves the majority of the population, groundwater stored in aquifers provides nearly 26% of New Jersey’s total water supply, playing an important role in less dense areas. An aquifer is an underground layer of water-saturated rock, sand, or gravel. These underground sources are categorized as either unconfined, meaning they are close to the surface, or confined, meaning they are trapped between less permeable layers.
The Coastal Plain, covering the southern half of the state, contains extensive confined aquifer systems, including the deep Potomac-Raritan-Magothy (PRM) Aquifer System. The PRM is a major source for large public water systems in the Camden metropolitan area and other parts of South Jersey. Conversely, the shallow, unconfined Kirkwood-Cohansey Aquifer System is the uppermost layer in the south, supplying water to domestic wells, agriculture, and the streams of the Pinelands.
Because the Kirkwood-Cohansey is unconfined, it is more susceptible to contamination from surface activities like agriculture and waste disposal. Confined aquifers, especially near the coast, face risks from saltwater intrusion when excessive pumping lowers the water pressure, allowing brackish water to move into the freshwater zone.
Geographic Distribution of Supply
The source of water for New Jersey residents is largely dictated by the state’s north-to-south geological structure and population density. The northern region, including the Highlands and Piedmont provinces, relies heavily on surface water due to its mountainous terrain and dense population centers. Large reservoir systems, like Wanaque and the Raritan Basin reservoirs, are strategically located in this area to capture runoff and supply millions of people.
Central New Jersey uses a mixed approach, leveraging both major surface water systems and localized aquifers. The Delaware and Raritan Canal acts as a central artery, delivering river water across the region. Local municipalities may supplement this supply with withdrawals from the PRM Aquifer System, providing redundancy and supporting the region’s suburban and industrial demands.
South Jersey, which lies entirely within the Coastal Plain, shows a near-exclusive dependence on groundwater. The flatter, sand-rich geology of this region makes the construction of large surface reservoirs impractical. The deep, extensive PRM Aquifer System provides the bulk of the potable water to major population centers. Meanwhile, the shallow Kirkwood-Cohansey Aquifer is the source for domestic wells and irrigation in the Pinelands and surrounding areas.
Water Treatment and Delivery Infrastructure
Once raw water is secured from a source, it enters a complex engineered system designed to make it safe for consumption and deliver it to the consumer. Treatment facilities employ processes like coagulation, filtration, and disinfection to remove suspended particles and harmful microorganisms. The water is often disinfected with chlorine or chloramine to maintain purity as it travels through the distribution system.
The New Jersey Water Supply Authority (NJWSA) operates major wholesale water systems, including the Raritan Basin and Manasquan systems, providing raw water to large utility companies. These companies, known as purveyors, treat the water and manage the final distribution to homes and businesses. Water movement across vast distances is accomplished through a network of pumping stations and large-diameter transmission lines.
The distribution network is a complex web of pipes, valves, and water mains that ensures pressurized water reaches every tap. This infrastructure requires constant maintenance, as aging systems can lead to water loss or vulnerability to contamination. The NJWSA, along with numerous private and public utility companies, manages this flow to meet the high demand of the state’s metropolitan areas.