Water Hardness Fact Sheet

Definition: The sum of the cations that have a charge greater than one and are present in the water.

Background:

  • Calcium (Ca2+) and Magnesium (Mg2+) are the most common ions that are found in hard water, while iron (Fe2+), Manganese (Mn2+) and Aluminum (Al3+) can also contribute to hardness.
  • Water acquires ions when it passes through soil and rock that contain rich mineral deposits. Sandstone, limestone, and siltstones are rich in calcium, while dolomites are rich in magnesium.
  • Hardness is measured in parts per million (ppm) or milligrams per liter (mg/L) and grains per gallon (gpg) of dissolved ions.

Environmental Impacts:

  • Calcium is needed for aquatic plant cell walls, shells, and bones of many aquatic organisms.
  • Magnesium is required for chlorophyll in plants
  • Hard water prevents fish from absorbing other toxic cations like lead, arsenic and cadmium.
  • Hard water usually has high alkalinity, which helps maintain the pH levels suitable for aquatic life.
  • Low (0-60 ppm) and very high hardness (>180 ppm) make it difficult for fish to regulate osmosis (balance between the amount of ions inside and outside of a fish's body).

Human Impact:

  • Hard water is not a pollutant and is not a major health concern for people; it is more of a non-health related nuisance.
  • The presence of the ions can clog pipes (but reduces corrosion of the pipes), cause film on sinks and bathtubs, and may affect the odor and flavor of the water.
  • People "soften" their water using filters or system exchanges that replace calcium and magnesium with sodium ions. Another method is the lime-soda process to remove ions.
  • Humans increase hardness when water runs through: mine sites, industrial areas that produce calcium and metals, and wastewater from households (by human waste and cleaning products).

Water Quality:

  • The Environmental Protection Agency (EPA) does not have a standard for overall water hardness or for the levels of calcium and magnesium levels, since they are not pollutants.
  • Water treatment plants regulate the water hardness allowing no more than 200 ppm calcium hardness and no more than 150 ppm magnesium.