Department of Environmental Conservation

D E C banner


Groundwater Resources of New York

Map showing Primary and Principal Aquifers in New York State
Groundwater Resources of New York State

This map shows the location of New York's most productive aquifers. Although bedrock formations are a significant source of groundwater supply, the most productive aquifers in New York are generally located in unconsolidated sediments (e.g., sand and/or gravel deposits). The areas shown in blue on the map are Primary Aquifers. These are aquifers that are capable of yielding a great deal of groundwater and are also heavily utilized. The green areas show the remainder of the unconsolidated aquifers in New York that are generally capable of providing 10 to 100 or more gallons per minute. These are termed Principal Aquifers and for the most part are not as heavily utilized as Primary Aquifers. Although other areas in upstate New York are capable of supplying groundwater, these delineated areas are the most reliable sources.

For a list of detailed aquifer map reports in upstate New York, go to the US Geological Survey (USGS) Detailed Aquifer Mapping (leaves DEC website).

Major Hydrologic Units of the Long Island Aquifer

The Long Island Aquifers, shown in light red, are among the most productive aquifers in the United States. While the rest of New York's aquifers are not as extensive as the Long Island aquifers, they are numerous and reliable sources of groundwater.

Bedrock aquifers are also an important source of groundwater. Most bedrock aquifers are not mapped in New York.

Statewide, New Yorkers use almost 900 million gallons per day of groundwater (USGS, 2000).

What is Groundwater?

Groundwater provides drinking water to one quarter of New Yorkers, and half of all Americans. Groundwater is an often misunderstood resource that provides drinking water to one quarter of New Yorkers, and half of all Americans. It can be found virtually everywhere on the planet at depths ranging from very shallow to very deep.

When rain falls to the ground, some of it is carried away as runoff down-slope into streams, lakes, and other bodies of water or into sewers. But some of it travels downward into the ground and through the underlying sediment, the upper part of which is not completely filled with water (the "unsaturated zone"). Continuing its downward route through the unsaturated zone, it moves through the interconnected openings of sand, gravel, silt, and clay or openings in rock until it reaches the "saturated zone" where it becomes groundwater.

For more groundwater basics, visit Aquifers and Groundwater (leaves DEC website) from the USGS.

Misconceptions about Groundwater

Misconception: Groundwater flows in underground streams and rivers.

Saturated zone map
Where does groundwater come from?

When you mention groundwater to many people, the image they see is one of vast underground rivers flowing like surface water. Underground flow in open channels rarely occurs, although we can see it in cave tours. The truth is that most groundwater occurs between grains of sand, gravel, silt, or clay (unconsolidated sediments) or in the fractures, bedding planes, and joints of bedrock.

Imagine a jug filled with marbles. Now pour water into the jug. The water is located in the spaces between the marbles. That's how groundwater exists in unconsolidated sediments. Or to understand groundwater in bedrock, take a large block of wood and drill some long holes through it. Now submerge the block in water. Water will be found mostly in the holes.

Misconception: Water can be found by dowsing, witching, or divining.

Controlled experiments have proven water witching and similar methods to be no more successful than choosing a drilling location randomly. Water witching, dowsing, or divining methods can appear to be successful because statistically speaking, almost any hole drilled in New York State will probably result in the discovery of some amount of water.

Misconception: Artesian well water always flows to the surface.

An "artesian aquifer" refers only to groundwater that is under pressure because confined by relatively impermeable sediments. Well water within such an aquifer will rise to its potential water level (also known as the potentiometric level). However, water will flow out of the top of the well only if the potentiometric level is higher than the top of the well.

Misconception: Artesian water is best.

As pointed out above, the term artesian applies to the pressure conditions of an aquifer. While the pressure does not affect the quality of water, artesian water may be less vulnerable to surface contamination because the overlying confining layers usually protect it.

Misconception: Groundwater is found only in aquifers.

A man dowsing for water

While water does not move quickly through sediment types such as clay or silt, groundwater does exist between their grains. And while a confining layer prevents water from moving through it quickly, water does move through it at a greatly reduced rate compared to a productive aquifer.

Misconception: Surface water is far more plentiful than groundwater in the world.

This is true only if we include the water in our world's oceans (which represents 97% of Earth's water) and frozen water (another 2%). Of the remaining 1% of the world's water, groundwater accounts for 96% while streams, lakes, and wetlands make up most of the other 4% and the rest is atmospheric water. Despite its abundance, much of the world's groundwater is not easily recovered.

Misconception: All groundwater or spring water is suitable for drinking.

When water flows through soil sediments there is a filtering effect. However, harmful bacteria are still capable of entering wells and springs. In addition, contamination from a variety of sources may occur and flow toward wells and springs. Finally, some natural conditions such as high levels of salt, radon, or sulfates may render water unsuitable for drinking.

Groundwater Resource Mapping

Canisteo Valley, New York

A GIS data set containing the mapping of 1:24,000 scale Primary and Principal Aquifers (leaves DEC website) is available at the NYS GIS Clearinghouse. Enhancements were made to these maps to create digital, georeferenced map layers. The digital map layers contain original mapping units and aquifer boundaries as well as new standardized mapping units and updated aquifer boundaries. The original published aquifer maps contain additional base and geologic information not included n these map layers.

Additionally a GIS coverage for 1:250,000 scale Principal Aquifers model is also available at the NYS GIS Clearinghouse.

Although many high yield bedrock formations exist in upstate New York, the most productive aquifers consist of unconsolidated deposits of sand and gravel that occupy major river and stream valleys or lake plains and terraces. These aquifers typically form flat areas that are suitable for development and generally provide an ample ground-water supply. Because of development, coupled with the high permeability of these deposits and shallow depth to the water table, makes these aquifers particularly susceptible to contamination from point sources, New York has issued regulations limiting the siting of landfills, oil and gas wells, and tire stockpiles over primary and/or principal source aquifers.

Click image to go to USGS webpages for larger
version of the map. (leaves DEC website)

To enhance and promote proper development, management, and protection of the unconsolidated aquifers of upstate New York, DEC has long partnered with the United States Geological Survey (USGS) to conduct research and publish reports on groundwater resources of the state. USGS also partners with various local agencies. The distribution and hydrogeologic characteristics of the unconsolidated aquifers are presented at the 1:250,000 scale in a series of five maps published in 1988 on a cooperative basis between the USGS and DEC. These reports are available on the USGS webpage "Unconsolidated Aquifers in Upstate New York, 1:250,000 Scale" (leaves DEC website)

Beginning in 1980 and continuing through today, the USGS has partnered with DEC and other entities to produce nearly 70 detailed hydrogeologic map reports for selected aquifers at the 1:24,000 scale. These aquifer map reports generally include a series of 1:24,000 scale maps showing aquifer boundaries, surficial geology, location of wells and test holes, aquifer thickness, the water-table or potentiometric surface, and pertinent discussion. You can select various areas of the map for additional details.

Typical geological cross section.

305(b) Groundwater Quality Basin Reports

Ambient Groundwater Monitoring Program

As an ongoing cooperative project between the NYSDEC Division of Water and the USGS, this program supports NYSDEC's federally designated responsibility to assess and report on the quality of New York's ground water as part of the requirements of the 305(b) section of the Clean Water Act Amendments of 1977. The objectives of the Ambient Groundwater Monitoring Program are: to assess and report on the quality of the state's groundwater; identify long-term groundwater quality trends; characterize naturally occurring or background conditions; and establish an initial statewide comprehensive groundwater quality baseline for future comparison. The program is designed so that all major drainage basins in the state are monitored once every five years.


The program started with a pilot study of the Mohawk River basin in 2002. This was followed up with a partial study of the Chemung River basin (2003) and full studies of Lake Champlain and Upper Susquehanna River basins (2004); St. Lawrence, Delaware and Genesee River basins (2005); and Alleghany, Lake Erie / Western Lake Ontario and Mohawk / Schoharie basins (2006). Studies of the Upper Hudson and Chemung River basins (2007); and Lower Hudson and Black River basins (2008) will complete the first full rotation of studies.

Study Basics

Each study-year a total of 60 wells are anticipated to be sampled. This number is then divided among the basins being studied. The final selection of wells attempts to achieve an equal split of public & private wells, an equal split of bedrock & overburden aquifer wells, and also an overall equal geographic distribution of wells. The majority of private wells considered for sampling are obtained from the DEC Water Well Program.

DEC and USGS plan the study cooperatively. USGS personnel conduct each study with oversight by DEC.

DEC's Pesticide Reporting Program provides funding in part to fulfill state pesticide monitoring requirements.

Sampling and analysis of groundwater includes field and physical parameters, bacteria, nutrients, inorganics, organics (including pesticides and VOCs), and radiochemicals.

Reports and Data

Data reports are developed by the USGS for each major basin and are available online at USGS's New York 305(b) Ambient Groundwater Quality Monitoring webpage (leaves DEC website) approximately one year after completion of respective studies. Resulting raw data is also available from the USGS through their National Water Information System (NWIS) website.

More Information

For more information on other DEC ongoing water quality monitoring efforts, please see our page on the Routine Statewide Monitoring Program.

More about Groundwater:

  • PDF Help
  • For help with PDFs on this page, please call 518-402-8086.
  • Contact for this Page
  • Bureau of Water Resource Management
    625 Broadway
    Albany, NY 12233-3508
    Send us an email
  • This Page Covers
  • Page applies to all NYS regions