Water Source

Long Island has a phenomenal natural drinking water resource situated deep below the surface of the earth. Called aquifers, these underground layers of highly porous sand, gravel, sediment or rock contain between 65 and 120 trillion gallons of one of life’s most precious resources. It is stored in three layers; the closest to the surface is the Upper Glacial Layer. Although no drinking water is taken from this section, it contains water that fell in the form of precipitation between 10 and 50 years ago.

The middle layer and largest of all the formations is the Magothy Aquifer. The majority of Nassau-Suffolk’s public drinking water, which can be as much as 1,000 years old, is drawn from here. Running from 200 to 1,000 feet deep, this layer of sand, gravel and silt was deposited about 60 million years ago.

A Raritan clay layer is found between the Lloyd and Magothy aquifers. Most scientists believe that gaps in this section allow some exchange of water between the two aquifers.

The Lloyd / North Shore Aquifer is the deepest and least used layer. Starting at 600 feet below the earth’s surface, this 200-foot layer is more than 1,800 feet deep in some areas and holds the oldest water—some of it more than 5,000 years! Approximately 90 percent of what is pumped by the Locust Valley Water District to meet consumer demand is drawn from the Lloyd / North Shore Aquifer, with the remaining coming from the Upper Glacial layer.


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