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Water Facts

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 our most precious resource.

Water Source

The source of the Locust Valley Water District’s groundwater is the Upper Glacial, North Shore, and Lloyd Aquifers, which are situated deep beneath the earth’s surface. 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.


Water is stored in three layers in the aquifers.

The Locust Valley Water District currently obtains its entire potable water supply from the North Shore, Lloyd and Upper Glacial formations through six supply wells drilled at six individual plant sites throughout its service area.

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

Between the Magothy Aquifer and the third, deepest layer is a Raritan clay layer. Most scientists believe that gaps in this section allow some exchange of water between the two aquifers.

The deepest and least-used layer is the Lloyd/North Shore Aquifer. Beginning 600 feet below the surface, this 200-foot layer is more than 1,800 feet deep at points and holds the oldest groundwater water, some of it precipitated more than 5,000 years ago!

Water Cycle

The water cycle, otherwise known as the hydrologic cycle, is the continuous flow of water between earth and sky, a constantly transitioning state of evaporation and precipitation. Precipitation creates runoff that travels over the earth’s surface to fill lakes and rivers. During this process, the water infiltrates through openings in the soil to replenish underground aquifers, traveling down through the ground at the rate of about one foot per day, a process that naturally cleanses groundwater of most impurities.

Distribution System

Your drinking water is pumped from 550 feet underground and delivered through 56 miles of interconnected water main to meet all local, state, and federal drinking water standards. The Locust Valley stores one million gallons of water in an elevated tower 310 feet above sea level. This storage not only uses gravity to pressurize the distribution system, but also serves to provide adequate pressure and flow in firefighting and/or other emergency uses.

Water Quality