Water described as "hard" is high in dissolved minerals, specifically calcium and
magnesium. Hard water is not a health risk, but a significant nuisance because of mineral buildup
on plumbing fixtures and poor soap and/or detergent performance.
Sources of Hardness Minerals in Drinking Water
Water is a good solvent and picks up impurities easily. Pure water - tasteless, colorless, and
odorless - is often called the universal solvent. When water is combined with carbon dioxide to form
very weak carbonic acid, an even better solvent results.
As water moves through soil and rock, it dissolves very small amounts of minerals and holds them
in solution. Calcium and magnesium dissolved in water are the two most common minerals that
make water "hard." The degree of hardness becomes greater as the calcium and magnesium
Indications of Hard Water
Hard water interferes with almost every cleaning task, from laundering and dishwashing to bathing
and personal grooming. Clothes laundered in hard water may look dingy and feel harsh and
scratchy. Dishes and glasses may be spotted when dry. Hard water may cause a film on glass
shower doors, shower walls, bathtubs, sinks, faucets, etc. Hair washed in hard water may feel sticky
and look dull. Water flow may be reduced by hard water deposits in pipes.
Dealing with hard water problems in the home can be a nuisance. The amount of hardness
minerals in water affects the amount of soap and detergent necessary for cleaning. Soap used in
hard water combines with the minerals to form a sticky soap curd. Some synthetic detergents are
less effective in hard water because the active ingredient is partially inactivated by hardness, even
though it stays dissolved. Bathing with soap in hard water leaves a film of sticky soap curd on the
skin. The film may prevent removal of soil and bacteria. Soap curd interferes with the return of skin
to its normal, slightly acid condition, and may lead to irritation. Soap curd on hair may make it dull,
lifeless and difficult to manage.
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. A sour odor can develop in clothes. Continuous laundering in hard water can
shorten the life of clothes.
In addition, soap curds can deposit on dishes, bathtubs and showers, and all water and plumbing
fixtures. Hard water also contributes to inefficient and costly operation of water-using appliances.
Heated hard water forms a scale of calcium and magnesium minerals that can contribute to the
inefficient operation or failure of water-using appliances. Pipes can become clogged with scale that
reduces water flow and ultimately requires pipe replacement.
Potential Health Effects
Hard water is not a health hazard. In fact, the National Research Council (National Academy of
Sciences) states that hard drinking water generally contributes a small amount toward total calcium
and magnesium human dietary needs. They further state that in some instances, where dissolved
calcium and magnesium are very high, water could be a major contributor of calcium and
magnesium to the diet.
Much research has been done on the relationship between water hardness and cardiovascular
disease mortality. Numerous studies suggest a correlation between hard water and lower
cardiovascular disease mortality. The National Research Council has recommended further studies
on this relationship.
Hard water treated with an ion exchange water softener has sodium added. According to the Water
Quality Association (WQA) the ion exchange softening process adds sodium at the rate of about 8
mg/liter for each grain of hardness removed per gallon of water. For example, if water has a
hardness of 10 grains per gallon, it will contain about 80 mg/liter of sodium after being softened with
an ion exchange softener if all hardness minerals are removed.
Because of the sodium content of softened water and potential benefits of drinking hard water,
some individuals may be advised by their physician not to install water softeners, to soften only hot
water, or to bypass the water softener with a cold water line (usually to a separate faucet at the
kitchen sink) to provide unsoftened water for drinking and cooking.
If you are on a municipal water system, the water supplier can tell you the hardness level of the
water they deliver. If you have a private water supply, you can have the water tested for hardness.
Many companies that sell water treatment equipment offer hardness tests. When using these water
tests, be certain you understand the nature of the test, the water condition being measured, and
the significance of the test results. An approximate estimate of water hardness can be obtained
without the aid of outside testing facilities. Water hardness testing kits are available for purchase. If
more accurate measurements are needed, obtain a laboratory test.
Interpreting Test Results
Water hardness often is expressed as grains of hardness per gallon of water (gpg) or milligrams of
hardness per liter of water (mg/L). Table I, adapted from the Water Quality Association (WQA),
shows hardness classifications. Hardness ions are typically combined with sulfate, chloride,
carbonate, or bicarbonate ions. For consistency, concentrations are generally converted to the
equivalent concentration as calcium carbonate (CaCO3) and expressed in terms of hardness as
The Environmental Protection Agency (EPA) establishes standards for drinking water which fall into
two categories - Primary Standards and Secondary Standards. Primary Standards are based on
health considerations and Secondary Standards are based on taste, odor, color, corrosivity,
foaming, and staining properties of water. There is no Primary or Secondary standard for water
Water hardness is classified by the U.S. Department of Interior and the Water Quality Association
Classification of water hardness (hardness as calcium carbonate).
There are two ways to help control water hardness; add a packaged or liquid softener to a batch of
water (washing machine or tub), or use an ion exchange water softening unit. Powdered or liquid
water softeners are chemicals that help control water hardness. They fall into two categories:
precipitating and non-precipitating.
Precipitating water softeners include washing soda and borax. These products form an insoluble
precipitate with calcium and magnesium ions. The mineral ions then cannot interfere with cleaning
efficiency, but the precipitate makes water cloudy and can build up on surfaces.
Precipitating water softeners increase alkalinity of the cleaning solution and this may damage skin
and other materials being cleaned. Non-precipitating water softeners use complex phosphates to
sequester calcium and magnesium ions. There is no precipitate to form deposits and alkalinity is
If used in enough quantity, non-precipitating water softeners will help dissolve soap curd for a
period of time. Ion exchange water softening units can be permanently installed into the plumbing
system to continuously remove calcium and magnesium.
Water softeners operate on the ion exchange process. In this process, water passes through a
media bed, usually sulfonated polystyrene beads. The beads are supersaturated with sodium. The
ion exchange process takes place as hard water passes through the softening material. The
hardness minerals attach themselves to the resin beads while sodium on the resin beads is
released simultaneously into the water.
When the resin becomes saturated with calcium and magnesium, it must be recharged. The
recharging is done by passing a salt (brine) solution through the resin. The sodium replaces the
calcium and magnesium which are discharged in the waste water. Softened water is not
recommended for watering plants, lawns, and gardens due to its sodium content.
Although not commonly used, potassium chloride can be used to create the salt brine. In that case
potassium rather than sodium is exchanged with calcium and magnesium. Before selecting an ion
exchange water softener, test water for hardness and iron content. When selecting a water
softener, the regeneration control system, the hardness removal capacity, and the iron limitations
are three important elements to consider.
There are three common regeneration control systems. These include a time-clock control (you
program the clock to regenerate on a fixed schedule); water meter control (regenerates after a
fixed amount of water has passed through the softener); and hardness sensor control (sensor
detects hardness of the water leaving the unit, and signals softener when regeneration is needed).
Hardness removal capacity, between regenerations, will vary with units. Softeners with small
capacities must regenerate more often. Your daily softening need depends on the amount of water
used daily in your household and the hardness of your water. To determine your daily hardness
removal need, multiply daily household water use (measured in gallons) by the hardness of the
water (measured in grains per gallon).
Example: 400 gallons used per day X 15 grains per gallon hardness = 6,000 grains of hardness
must be removed daily.
Iron removal limitations will vary with water softener units. If the iron level in your water exceeds the
maximum iron removal capacity recommended by the manufacturer of the unit you are considering,
iron may foul the softener, eventually causing it to become plugged. If the manufacturer does not
identify an iron removal capacity, assume the capacity to be zero.
Hard water is not a health hazard, but dealing with hard water in the home can be a nuisance. The
hardness (calcium and magnesium concentration) of water can be approximated with a home-use
water testing kit, or can be measured more accurately with a laboratory water test.
Water hardness can be managed with powdered or liquid water softeners or with an ion exchange
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