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Water Hardness

DEP gets many questions about water hardness from people who are installing dishwashers, hot-water heaters, and various other equipment that use water. Hardness is a measure of the dissolved natural minerals calcium and magnesium. The more natural minerals, the harder the water is. Neighborhoods in New York City receive their public water from upstate reservoirs in the Catskill/Delaware watershed, the Croton watershed, or a blend from both sources. Water from the Croton supply is considered “moderately hard,” while the Catskill/Delaware supply is considered “soft” or “slightly hard.”

Beginning in 2018, DEP anticipates a greater use of water from the Croton supply due to planned infrastructure projects designed to improve the resiliency of NYC’s water supply. As a result, water in several areas of the City may become a bit harder. The water remains of excellent quality and is safe to drink. However, water hardness may affect the efficiency of some equipment. You should consult the owner’s/operator’s manual for the device you are operating to determine the effect, if any, of water hardness.

To help you determine whether you are in an area of the City that could receive moderately hard water, visit Croton Water Distribution Maps.

Frequently Asked Questions

What is hard water?

  • Hard water contains a high amount of naturally occurring minerals and dissolved solids, particularly calcium and magnesium. The higher the content of calcium and magnesium, the harder the water.
  • While hard water can leave water spots on shower doors and buildup on plumbing fixtures, it is safe to drink (in fact, calcium carbonate is the same mineral found in calcium vitamin supplements).

How does water become hard?

  • As water moves through soil and rocks it easily dissolves small amounts of minerals and holds them in solution.

How is hardness measured?

  • Water hardness is determined by the amount of calcium carbonate (CaCO3) it contains.

Is NYC water hard?

  • Neighborhoods in New York City receive their public water from upstate reservoirs in the Catskill/Delaware watershed, the Croton watershed, or a blend from both sources. Water from the Croton supply is considered “moderately hard”, while the Catskill/Delaware supply is considered “soft” or “slightly hard”. Citywide average hardness is about 1.8 grain/gallon (CaCO3). In areas of the City where Catskill/Delaware and Croton water supplies are blended, the hardness can reach 7 grain/gallon (CaCO3).
  • To help you determine whether you are in an area of the City that could receive moderately hard water, visit Croton Water Distribution Maps.

What are common signs of hard water?

  • Hard water can interfere with cleaning tasks—from doing laundry and washing dishes to bathing and hair washing. Some telltale signs of hard water include:
  • White scaly spots on your car after washing it.
  • Soap scum or film on glass shower doors, shower walls, sinks and faucets, typical “ring around the bathtub.”
  • Reduced water flow due to hard-water deposits inside pipes (scale).

How can I reduce the effects of hard water scale?

If hardness scale becomes a problem there are a number of simple measures that can be taken to reduce the level of deposition:

  • Leave a squeegee inside the shower and have each family member squeegee the walls and shower door after each use. This reduces hard-water buildup and a whole lot of scrubbing later on.
  • Try applying plain white vinegar and lemon juice—acids that help loosen and remove hard water deposits from glass shower enclosures.
  • If your showerhead plugs up from hardness, fill a sandwich bag with vinegar and use a rubber band to fasten the bag around your showerhead. Leave it overnight.
  • Pour a cup of white vinegar in the toilet bowl and leave it there overnight. Flush in the morning.
  • Reduce the temperature of your hot water to 60°C or lower to decrease the build-up of scale.
  • Follow the manufacturer’s instructions for any appliances that use water.