What Is Hard Water? In Plain Words

What hard water is

The USGS says the simple definition of water hardness is the amount of dissolved calcium and magnesium in the water.

Hard water is high in dissolved minerals, largely calcium and magnesium.

The USGS also says hardness is caused by compounds of calcium and magnesium, and by a variety of other metals.

How water picks up those minerals

The USGS says water systems using groundwater as a source are concerned with water hardness, since as water moves through soil and rock it dissolves small amounts of naturally-occurring minerals and carries them into the groundwater supply.

The USGS says water is a great solvent for calcium and magnesium, so if the minerals are present in the soil around a water-supply well, hard water may be delivered to homes.

Nebraska Extension words it the same way: water is a good solvent and picks up impurities easily, and as water moves through soil and rock, it dissolves very small amounts of minerals and holds them in solution. Nebraska Extension says dissolved calcium and magnesium are the two most common minerals that make water hard, and the degree of hardness becomes greater as the calcium and magnesium content increases.

How hardness is measured

The USGS gives general guidelines for classification of waters, measured in mg/L (milligrams per liter) as calcium carbonate:

• Soft: 0 to 60 mg/L as calcium carbonate
• Moderately hard: 61 to 120 mg/L as calcium carbonate
• Hard: 121 to 180 mg/L as calcium carbonate
• Very hard: more than 180 mg/L as calcium carbonate

That scale is the whole measurement on this page. If a report gives you a number in mg/L as calcium carbonate, you can place it in one of those four groups.

Hard water and soft water, in one line: on the USGS scale, soft water is 0 to 60 mg/L as calcium carbonate, and water above that range is classed as moderately hard, hard, or very hard.

Where hard water is found

The USGS says water hardness varies throughout the United States.

For its national map, the USGS gives these cautions: the data illustrated represent water hardness on a national and regional scale and must be so interpreted; the 1975 data are not designed to be used to make local decisions or decisions on the scale of individual homeowner property; and information that is directly relevant to water hardness and other chemical properties at a home or immediate locale should be provided by the local health agency or local water utility.

The USGS also notes, for that map, that major-ion chemistry in groundwater is relatively stable and generally does not change over time, and that although the map illustrates data from 1975, these data have been found to be accurate and useful in current assessments.

Signs hard water can leave at home

The USGS says you may have felt the effects of hard water the last time you washed your hands: depending on the hardness of your water, after using soap to wash you may have felt like there was a film of residue left on your hands.

The USGS says, in hard water, soap reacts with the calcium (which is relatively high in hard water) to form “soap scum,” and when using hard water, more soap or detergent is needed to get things clean, be it your hands, hair, or your laundry.

• Dishes and glassware: The USGS says one of the most common causes of cloudy dishes and glassware is hard water, and that glasses taken out of the dishwasher may show spots or film. The USGS calls this hard-water residue “not dangerous, but unsightly.”
• Scale when water is heated: The USGS says when hard water is heated, such as in a home water heater, solid deposits of calcium carbonate can form. The USGS calls this scale, and says this scale can reduce the life of equipment, raise the costs of heating the water, lower the efficiency of electric water heaters, and clog pipes. The USGS also says mineral buildup will occur in a home coffee maker.
• Scale inside pipes: The USGS says long-term movement of hard water through a pipe can result in scale buildup, and water pipes can gradually close up resulting in less water movement through the pipe and a lowering of water pressure.
• Laundry and fabrics: The USGS says hard water can shorten the life of fabrics and clothes. Nebraska Extension adds that, when doing laundry in hard water, soap curds lodge in fabric during washing to make fabric stiff and rough, incomplete soil removal from laundry causes graying of white fabric and the loss of brightness in colors, and continuous laundering in hard water can shorten the life of clothes.
• Soap curd on skin, hair, dishes, and fixtures: Nebraska Extension says soap curd on hair may make it dull, lifeless, and difficult to manage, and soap curds can deposit on dishes, bathtubs and showers, and all water and plumbing fixtures.

What the official sources say about health

Nebraska Extension says, in its opening summary: “Hard water isn’t a health hazard but can be a nuisance within the home.” In its main text it says water described as “hard” contains high amounts of dissolved calcium and magnesium, and that hard water is not a health risk but can be a nuisance because of mineral buildup on plumbing fixtures and poor soap and/or detergent performance.

The USGS, on the spots and film left on dishes and glassware, says that residue is “not dangerous, but unsightly.”

The USGS also notes a benefit side, as it words it: humans need minerals to stay healthy, and the World Health Organization (WHO) states that drinking-water may be a contributor of calcium and magnesium in the diet and could be important for those who are marginal for calcium and magnesium intake.

This page prints those statements as the sources word them. It adds no health claim of its own in either direction.

What the EPA secondary standards page does, and does not, say

The U.S. Environmental Protection Agency (EPA) page “Secondary Drinking Water Standards: Guidance for Nuisance Chemicals” says EPA has established National Secondary Drinking Water Standards that set non-mandatory water quality standards for 15 contaminants, that EPA does not enforce these “secondary maximum contaminant levels” (SMCLs), that they are established as guidelines to assist public water systems in managing their drinking water for aesthetic considerations, such as taste, color, and odor, and that these contaminants are not considered to present a risk to human health at the SMCL.

The EPA table on that page lists these contaminants: Aluminum, Chloride, Color, Copper, Corrosivity, Fluoride, Foaming agents, Iron, Manganese, Odor, pH, Silver, Sulfate, Total Dissolved Solids (TDS), and Zinc. Hardness, calcium, and magnesium are not listed in that table as a separate contaminant.

The one place the word “hardness” appears in that EPA table is in the row for Total Dissolved Solids (TDS), whose secondary standard is listed as 500 mg/L, and whose noticeable effects above the secondary level are listed as: “hardness; deposits; colored water; staining; salty taste.”

How to find the hardness of your own water

Start with your water provider’s annual report. Nebraska Extension says public water system operators are required to provide annual water quality reports, referred to as consumer confidence reports (CCRs). Nebraska Extension says the CCR may include information about the hardness level of the water delivered, and you can also contact the water supplier and ask for this information.

If you have a private water supply, use a laboratory test. Nebraska Extension says, if you have a private water supply, you can have the water tested for hardness, and that most water testing laboratories offer hardness tests for a fee. Its summary says the hardness of water can be measured more accurately with laboratory water analysis.

Use that route — your provider’s CCR, your local health agency or local water utility, or a laboratory test — for a number that is about your home. A national map and the signs listed above cannot give you that local number.