Public Water Supply

Public Water Supply

Where does Nassau County’s drinking water come from?

Nassau County gets all its drinking water from the water stored in the porous soil beneath Long Island. This fresh water source is called ground water. The geological formations which store the large quantities of water are called aquifers. 

Nassau County uses three major aquifers for its drinking water. The uppermost is called the Upper Glacial aquifer. Directly below the Upper Glacial aquifer is the Magothy aquifer. The Magothy aquifer is the largest aquifer and is where most of Nassau County’s drinking water is supplied from. The third aquifer is called the Lloyd aquifer. The Lloyd aquifer is separated from the bottom of the Magothy aquifer by the impervious Raritan Clay formation which protects it from contamination. This aquifer is reserved for use mainly in areas such as the south shore barrier islands where the upper aquifers have been infiltrated by saltwater intrusion. Beneath the Lloyd aquifer lies the bedrock. The bedrock is located about 200 feet below sea level on the north shore decreasing to 1600 feet on the south shore. 



Nassau County Public Water Systems

publicwatersupplyimage2The majority of the drinking water in Nassau County is delivered to the homes and businesses by public water systems. There are 46 public water systems and approximately 500 private wells in Nassau County. 

The components of a typical public water system consists of wells which withdraw the water from the ground, treatment facilities to re-move any impurities from the water, storage tanks to store the water and to maintain constant water pressure in the system, and a distribution system which consists of a network of pipes called water mains to carry the water to homes, businesses, and fire hydrants.

For a list of Community Water Systems and their phone numbers, click here.

Nassau County Potable Water Safety, Testing, and Your Right to Know

Public water systems are routinely tested by both the public water supplier and the Nassau County Department of Health. Wells, treatment facilities, water storage tanks, and the distribution systems are tested for over 150 different contaminants. The contaminants tested for include microbiological, Volatile Organic Contaminants (VOC), pesticides, inorganic contaminants, nitrates, perchlorate, radiological, disinfection byproducts and asbestos. Each contaminant has a specific sampling cycle in which it is required to be tested. Some of the testing requirements in Nassau County are much more extensive than that required by either New York State or the Federal Government.

Public supply wells that do not meet the Maximum Contaminant Level (MCL) for a contaminant must be removed from service or treated to remove the contaminant prior to the water being delivered to your home. To protect public health, all of the water delivered to your home meets the standards established by the Environmental Protection Agency, New York State Department of Health and Nassau County Department of Health.


Bottled water must meet the same MCL standards as your public water supply, however, is not required to be tested as extensively as the drinking water in Nassau County. Some bottled waters, such as those classified as mineral, flavored, vitamin waters, etc., do not fall under the “Drinking Water” classification and may be exempted from meeting all quality standards as required for potable drinking water. Bottled water can cost 1000 times more than your tap water.

As a consumer you have a right to know about your drinking water quality. Your Annual Water Quality Report (AWQR) provides testing results. You may contact your public water supplier for their latest AWQR.

Is my water safe to drink?

The water supplied to you is routinely tested by both your public water system and the Nassau County Health Department for compliance with the New York State Sanitary Code, Part 5 drinking water standards or maximum contaminant levels (MCLs). Testing is performed at operating wells and at representative locations throughout the distribution system. Your public water system distributes each year the Annual Water Quality Report that summarizes water testing performed in the distribution system and a complete description of the operation including water conservation measures you can take and billing information.

My water has a problem with taste, odor or rust. Is it safe?

The conditions are of an aesthetic, not health, nature. Please contact your water supplier if you are experiencing these conditions. Water systems in Nassau County can usually resolve these conditions in a short period of time.

Do I need to have my water tested for lead?

Lead is found in water as the result of contact with lead plumbing or lead solder in your home's plumbing system. Lead levels increase in proportion to the time that water stays in piping. The United States Environmental Protection Agency (USEPA) recommends that piping that is not used for more than six hours be flushed, for up to two minutes or until the water gets colder, to eliminate any lead which may have leached out of the plumbing.

Do I need a filter?

Filters are not necessary for homes that are supplied by public water systems. Public water systems are routinely tested and meet drinking water standards set by the Federal and State Governments. If you still wish to install a filter, be certain to install a filter with a flow indicator and to strictly follow the manufacturer's recommendations for maintenance.

Do I need to drink bottled water?

There is no need to use bottled water instead of tap water. Bottled water in New York State must meet the same water quality requirements of the New York State Sanitary Code that apply to tap water. Please be sure that the label has been certified by the New York State Health Department for sale. The certification identification is on the label as "NYSHDCERT #000". This assures that the water meets New York State requirements.

What if I have a complaint about drinking water?

Your local water supplier handles complaints about rusty water or odors. Other inquiries may be made to the Health Department Bureau of Water Supply at 227-9692 weekdays from 9:00 a.m. to 4:45 p.m. For emergencies after business hours, call 742-6154.

How You Can Protect Our Water Supply

Responsibility for the regulation and operation of public water supplies rests with government agencies and public utilities. However, responsible citizens can have a significant influence on the supply of adequate and safe water for their communities. There are several important ways in which you can and should participate.

  • Never pour chemicals into storm drains or on the ground. Contact your Town or City S.T.O.P Program for information on disposal locations.
  • Report individuals who pour chemicals into storm drains or on the ground.
  • Use fertilizers and pesticides only when needed and as little as possible.
  • Become involved in protecting and conserving your community’s water supply.
  • Use proper back-flow prevention devices wherever underground sprinklers or aerosol chemical sprayers are used.
  • Properly remove or abandon in place aging underground heating oil tanks.
  • Support water conservation programs.
  • Support curricula in your schools which include a study of Long Island’s ground water system and water supply.
  • Conserve water at home and at the same time save money on water and water heating bills. This can be done by:
  • Keep a bottle of tap water in the refrigerator.
  • Follow the restrictions on the outdoor use of water including odd and even day lawn sprinkling during the specified hours. Use rain sensors on automated sprinkler systems.
  • Making sure that your home’s plumbing is in proper repair and insulate the pipes to get both cool and hot water faster and more economically.
  • Use full loads in both clothes and dishwashers.
  • Use less water by showering rather than bathing.
  • Reset the tank float in older toilets to use less water.

Nassau County Groundwater Protection

Sources of ground water contamination have been identified and remediated for many years in Nassau County. Some of the remedial actions taken by the County are:

  • Regulation of population density and exclusion of industrial discharges in special ground water protection areas
  • County-wide sanitary sewers
  • Ban on sale and use of cesspool cleaners containing certain organic chemicals
  • Inspection and replacement of underground gasoline and petroleum storage tanks
  • Encouraging homeowners to properly remove or abandon in place aging underground heating oil tanks
  • Control of industrial wastewater discharges
  • Phasing out of municipal landfills
  • Elimination of open storage of road salting compounds
  • Regulation of the storage and handling of toxic and hazardous materials.
  • Elimination of underground injection of hazardous wastes

Backflow Prevention

What is a backflow prevention device?

The backflow prevention device is a complex mechanical unit that prevents the reversal of water flow and subsequent contamination of the water supply from irrigation systems, etc. This may occur when there is a loss of water pressure in the street water main due to a water main break, over pumping of fire hydrants or a generalized system pressure loss. Homeowners may be required to install a backflow prevention device if they have an in-ground irrigation system, solar heating system or a private well on their property.

Why do I need to test my backflow prevention device every year?

The New York State Sanitary Code, Part 5 and the Nassau County Public Health Ordinance require annual testing of the unit to confirm proper function. A listing of New York State Health Department Certified Testers is available at your public water supply office.

Who do I call for more information about backflow prevention device installations?

You may call your public water supplier to determine if a backflow prevention device is needed and to determine the type of device required. If you have additional questions you may call the Office of Water Supply Operations at (516) 227-9692.

Additional information and Resources

More information regarding your drinking water may be obtained by contacting your water supplier or by calling this Department at (516) 227-9692.

U.S. Environmental Protection Agency

NYS Department of Health Drinking Water Protection Program