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Irrigation Association of New York

Long Island Water – Where does it come from?

The Long Island water that comes out of our faucets originates far below the earth’s surface, in deep interconnected underground layers of sand, gravel and silt called aquifers. The water they contain consists entirely of what originated as rain that seeped slowly downward for hundreds or even thousands of years

The plentiful aquifers contain about 90 trillion gallons of water, enough to cover Long Island in a 300-foot flood, much more than is actually needed to meet our current demands. The unique system makes us less dependent on yearly rainfall as some other areas, such as New York City, for example, which relies on reservoirs for its public water. Our water source, constantly replenished by precipitation, has many unique benefits. Starting as rainwater, it seeps through hundreds of feet of soil and closely packed natural particles before reaching the aquifers. This procedure is actually a natural filtration process which cleanses the water of most impurities.

The water is stored by nature primarily in three underground layers. The top one, called the glacial layer, contains water that fell somewhere between 10 and 50 years ago. It is the newest to the groundwater system. Next is the Magothy layer, the largest of the aquifer formations. It holds the most water, much of it hundreds of years old. Running as deep as 800 feet, this layer of sand, gravel and silt was deposited about 60 million years ago and is the region’s main source of drinking water. The very deepest and oldest is called the Lloyd Aquifer, starting approximately 1,100 feet below the surface. This aquifer is largely untapped. It holds the oldest water; some of it has been there for more than 5,000 years. Some 1,000 deep wells throughout Nassau-Suffolk pump about 125 billion gallons of water from our aquifer system each year for use by the area’s 2.7 million residents. Surprisingly, more water is replenished by rainfall than is actually pumped. Obviously, we are not going to run out of water anytime soon, although we should make a conscious effort not to waste the natural resource. Although Long Island’s quantity of water is plentiful and its quality is among the best in the nation, you should be reminded that the future of our supply will be determined by how well we treat our environment today.

Paul J. Granger, P.E. is superintendent of the Port Washington Water District