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| Sources of Hardness
Minerals in Drinking Water |
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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
content increases and is related to the concentration
of multivalent actions dissolved in the water. |
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| Every
household and every factory uses water, and none
of it is pure. |
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| One
class of impurity that is of special interest is "hardness". This refers
to the presence of dissolved ions, mainly of calcium
Ca 2+ and magnesium Mg 2+ which are acquired through
contact with rocks and sediments in the environment.
The positive electrical charges of these ions are balanced
by the presence of anions (negative ions), of which
bicarbonate HCO 3 – and carbonate
CO 3 2– are most important. These ions have their
origins in limestone sediments and also from carbon
dioxide which is present in all waters exposed to the
atmosphere and especially in groundwaters. |
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| Indications
of Hard Water |
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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 deposits in pipes. |
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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 waterleaves 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. |
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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 inclothes.
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 fixtures. |
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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 |
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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. |
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Researchers have studied
water hardness and cardiovascular disease
mortality. Such studies have been "epidemiological
studies," which are statistical relationship
studies. |
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While some studies suggest
a correlation between hard water and lower
cardiovascular disease mortality, other
studies do not suggest a correlation. The
National Research Council states that results
at this time are inconclusive and recommends
that further studies should be conducted |
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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.
Most water testing laboratories offer
hardness tests for a fee, including
the Environmental Quality Center. Also
many companies that sell water treatment
equipment offer hardness tests. When
using these water tests, be certain
you understand thenature 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
through water testing upplycompanies.
If more accurate measurements are needed,
contact a testing laboratory. |
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| Interpreting
Test Results |
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The hardness
of your water will be reported
in grains per gallon, milligrams
per liter (mg/l) or parts per
million (ppm). One grain of hardness
equals 17.1 mg/l or ppm of hardness. |
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The Environmental
Protection Agency (EPA) establishes
standards for drinking water
which fall into two categories
-- Primary Standards and Secondary
Standards. |
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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
hardness. Water hardness is classified
by the U.S. Department of Interior
and the Water Quality Association
as follows: |
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NOTE: Other organizations may use
slightly different classifications. |
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| There
are two ways to help control water hardness: use
a packaged water softener or use a mechanical water
softening unit. |
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| Packaged water softeners
are chemicals that help control water hardness. They
fall into two categories: precipitating and
non-precipitating. |
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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. |
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Non-precipitating
water softeners use complex phosphates to sequester
calcium and magnesium ions. There is no precipitate
to form deposits and alkalinity is not increased.
If used in enough quantity, non-precipitating water
softeners will help dissolve soap curd for a period
of time. |
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Mechanical 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. 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. |
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For
example , if the water has a hardness of 10 grains per gallon,
it will contain about 80 mg/liter of sodium after
being softened in an ion exchange water softener
if all hardness minerals are removed. |
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Because of the sodium content
of softened 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 to provide unsoftened water
for drinking and cooking; usually to a separate faucet
at the kitchen sink. |
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| Softened water is not recommended
for watering plants, lawns, and gardens due to its
sodium content. |
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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. |
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Before selecting a mechanical
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. |
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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). |
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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). |
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Example: 400 gallons used per day X 15 grains per gallon hardness
= 6,000 grains of hardness must be removed daily. |
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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. |
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| Below
is a diagram of our Softener. It shows how our softener,
and everyone else’s,
works. |
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| A water softener is
an ion exchanger. |
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Hard
water—water with a high
calcium/magnesium content—enters the softener through
the “In” port indicated by the
green arrow. It passes through the control valve and into the
tank, where it goes from top to bottom through a specially
prepared resin that “softens” it. |
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The
resin consists of specially manufactured beads that have
been saturated with sodium ions. “Softening” occurs
as the hardness minerals in the water attach themselves to
the resin and are “exchanged” for sodium. |
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The softened water then enters the
long center tube, called a riser, via the strainer basket in
the bottom of the tank and passes upward through the riser.
The water exits the softener via the control valve (blue arrow)
and is sent to the home. |
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When the resin becomes saturated
by hardness minerals, the softener automatically goes into
regeneration. (The regeneration process is initiated by a timer
or a meter, depending on the type of softener you purchase.)
By this process the hardness minerals are washed down the drain
(via a drain tube not shown in the diagram), and the resin
bed is rinsed, resettled, and recharged with sodium. It is
now again ready to soften your water. |
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The regeneration
process is accomplished by passing very salty water from the
brine tank through the resin. The brine tank must remain filled
with softener salt at all times so that it can regenerate the
softening resin again and again Water Softeners Make Water
Work Better |
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| Water Softeners
Make Water Work Better |
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Water
softeners combat this nuisance by eliminating the minerals
that cause hard water. The most common kind of water softener
is a mechanical appliance plumbed directly into the home’s
water supply intake. (See figure 1) The water softener exchanges
calcium and magnesium with sodium in a process called ion
exchange. |
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The water softening
system consists of a mineral tank and a brine tank. The water
supply pipe is connected to the mineral tank so that water
coming into the house must pass through the tank before it
can be used. |
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The mineral tank holds
small beads (also known as resin) that carry a negative electrical
charge. The positively charged calcium and magnesium (called
ions) are attracted to the negatively charged beads. This attraction
makes the minerals stick to the beads as the hard water passes
through the mineral tank. (See figure 3.) |
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Eventually the surfaces of the beads
in the mineral tank become coated with the calcium and magnesium
minerals. To clean the beads, a strong sodium (salt) solution
held in the brine tank is flushed through the mineral tank.
Sodium ions also have a positive electrical charge, just not
quite as strong as that of calcium and magnesium. This large
volume of sodium ions overpowers the calcium and magnesium
ions and drives them off of the beads and into the solution.
The sodium solution carrying the minerals is then drained out
of the unit. Some sodium ions remain in the tank attached to
the surfaces of the beads |
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| Conventional
water softening |
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Most
conventional water-softening devices depend on a process
known as ion-exchange in which "hardness" ions
trade places with sodium and chloride ions that are loosely
bound to an ion-exchange resin or a zeolite (many zeolite minerals
occur in nature, but specialized ones are often made artificially.) |
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The
illustration depicts a negatively-charged zeolite to which
[positive] sodium ions are attached. Calcium or magnesium
ions in the water displace sodium ions, which are released
into the water. In a similar way, positively-charged zeolites
bind negatively-charged chloride ions (Cl –), which get displaced by bicarbonate ions
in the water. As the zeolites become converted to their Ca
2+ and HCO 3 – forms they gradually lose their effectiveness
and must be regenerated. This is accomplished by passing a
concentrated brine solution though them, causing the above
reaction to be reversed. Herein lies one of the drawbacks of
this process: most of the salt employed in the regeneration
process gets flushed out of the system and and is usually released
into the soil or drainage system— something that can
have damaging consequences to the environment, especially in
arid regions. For this reason, many jurisdications prohibit
such release, and require users to dispose of the spent brine
at an approved site or to use a commercial service company. |
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The
normal water softening cycle operates like this: Hard water
enters the mineral tank. Inside the tank, the calcium and
magnesium ions carried in the water attach themselves to
the beads. The surfaces of the beads eventually hold their
limit of calcium and magnesium and can’t remove
any more from the water. At this point the water softener must
be "regenerated". (See figure 2.) The three-step regeneration
cycle can be scheduled according to a timer or by a flow detection
meter. |
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The
first step, called the backwash phase, reverses the water’s
flow and flushes any accumulated dirt particles out of the
tank and down the drain. Next, in the regeneration or recharge
phase, the sodium rich brine solution flows from the brine
tank into and through the mineral tank. The brine washes
the calcium and magnesium off the beads. In the final phase,
the mineral tank is flushed of the excess brine, which now
also holds the calcium and magnesium, and the solution is
disposed of down the drain. |
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Sodium ions from the previous regeneration
cycle cling to the beads. Now when the hard water flows into
the mineral tank, the calcium and magnesium ions change places
with the sodium ions on the resin. The displaced sodium ions
remain issolved in the water. |
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