• Hard water is water that has high mineral
• Hard drinking water is generally not harmful
to one's health, but can pose serious problems
in industrial settings, where water hardness is
monitored to avoid costly breakdowns in
boilers, cooling towers, and other equipment
that handles water. In domestic settings, hard
water is often indicated by a lack of suds
formation when soap is agitated in water, and
by the formation of limescale in kettles and
water heaters. Wherever water hardness is a
concern, water softening is commonly used to
reduce hard water's adverse effects.
SOURCE OF HARDNESS
Water's hardness is determined by the concentration of multivalent cations
in the water. Multivalent cations are cations (positively charged metal
complexes) with a charge greater than 1+. Usually, the cations have the
charge of 2+. Common cations found in hard water include Ca2+ and Mg2+.
These ions enter a water supply by leaching from minerals within an aquifer.
Common calcium-containing minerals are calcite and gypsum. A common
magnesium mineral is dolomite (which also contains calcium). Rainwater and
distilled water are soft, because they contain few ions.
The following equilibrium reaction describes the dissolving/formation of
calcium carbonate scale:
CaCO3 + CO2 + H2O ⇋ Ca2+ + 2HCO3−
Calcium carbonate scale formed in water-heating systems is called limescale.
Calcium and magnesium ions can sometimes be removed by water softeners.
Temporary hardness is a type of water hardness caused by the
presence of dissolved bicarbonate minerals (calcium
bicarbonate and magnesium bicarbonate). When dissolved these
minerals yield calcium and magnesium cations (Ca2+, Mg2+) and
carbonate and bicarbonate anions (CO32-, HCO3-). The
presence of the metal cations makes the water hard. However,
unlike the permanent hardness caused by sulfate and chloride
compounds, this "temporary" hardness can be reduced either by
boiling the water, or by the addition of lime (calcium hydroxide)
through the softening process of lime softening.
Permanent hardness is hardness (mineral content) that cannot
be removed by boiling. When this is the case, it is usually caused
by the presence of calcium sulfate and/or magnesium sulfates
in the water, which do not precipitate out as the temperature
increases. Ions causing permanent hardness of water can be
removed using a water softener, or ion exchange column
EFFECTS OF HARD WATER
With hard water, soap solutions form a white precipitate (soap scum) instead of
producing lather, because the 2+ ions destroy the surfactant properties of the soap by
forming a solid precipitate (the soap scum). A major component of such scum is calcium
stearate, which arises from sodium stearate, the main component of soap:
2 C17H35COO- + Ca2+ → (C17H35COO)2Ca
Hardness can thus be defined as the soap-consuming capacity of a water sample, or the
capacity of precipitation of soap as a characteristic property of water that prevents
the lathering of soap. Synthetic detergents do not form such scums.
A portion of the ancient Roman Eifel aqueduct in Germany.
Hard water also forms deposits that clog plumbing. These deposits, called "scale", are
composed mainly of calcium carbonate (CaCO3), magnesium hydroxide (Mg(OH)2), and
calcium sulfate (CaSO4). Calcium and magnesium carbonates tend to be deposited as
off-white solids on the inside surfaces of pipes and heat exchangers. This precipitation
(formation of an insoluble solid) is principally caused by thermal decomposition of
bicarbonate ions but also happens to some extent even without such ions. The resulting
build-up of scale restricts the flow of water in pipes.
We have used running water as an energy source for thousands
of years, mainly to grind corn.
The first house in the world to be lit by hydroelectricity was
Cragside House, in Northumberland, England, in 1878.
In 1882 on the Fox river, in the USA, hydroelectricity produced
enough power to light two paper mills and a house.
Nowadays there are many hydro-electric power stations,
providing around 20% of the world's electricity.
The name comes from "hydro", the Greek word for water.
HOW IT WORKS
A dam is built to trap water, usually
in a valley where there is an
Water is allowed to flow through
tunnels in the dam, to turn
turbines and thus drive
Notice that the dam is much
thicker at the bottom than at
the top, because the pressure of
the water increases with depth.
Hydro-electric power stations can
produce a great deal of power
Gravitational potential energy is stored in the water
above the dam.
Because of the great height of the water, it will
arrive at the turbines at high pressure, which
means that we can extract a great deal of energy
from it. The water then flows away downriver as
In mountainous countries such as Switzerland and
New Zealand, hydro-electric power provides
more than half of the country's energy needs.
An alternative is to build the station next to a fastflowing river. However with this arrangement
the flow of the water cannot be controlled, and
water cannot be stored for later use.
• Once the dam is built, the energy is virtually free.
• No waste or pollution produced.
• Much more reliable than wind, solar or wave power.
• Water can be stored above the dam ready to cope with peaks in demand.
• Hydro-electric power stations can increase to full power very quickly,
unlike other power stations.
• Electricity can be generated constantly.
• The dams are very expensive to build.
However, many dams are also used for flood control or irrigation, so
building costs can be shared.
• Building a large dam will flood a very large area upstream, causing
problems for animals that used to live there.
• Finding a suitable site can be difficult - the impact on residents and the
environment may be unacceptable.
• Water quality and quantity downstream can be affected, which can have
an impact on plant life.
WHAT IS WATER
The process in which waste
water is treated to remove
solids and certain
impurities, and used in
irrigation or to recharge
groundwater aquifers is
called water recycling. It
wastewater sent from a
home or business through
a pipeline system to a
treatment facility, where it
is treated to a level
consistent with its
intended use. The is then
routed directly to a
recycled water system for
uses such as irrigation or
HOW IS IT DONE?
Treatment of wastewater is actually a remarkably
simple process that utilizes very basic physical,
biological and chemical principles to remove
contaminants from water.
The three steps involved in the treatment of
wastewater are:o Physical Systems- In physical processes raw
sewage passes through bar screens and grit
chamber. These physical processes remove
approximately half of the contaminants in
o Biological Systems- It converts non-settleable
solids to settleable solids which removes the rest
of the contaminants from the wastewater.
o Chemical System- Chemical system such as
chlorine contact chambers are used to kill the
remaining microorganisms not captured in final
clarifiers. The point where treated water is
discharged into a stream or body of water is
called the outfall.
Recycled water can be used for
It can be used by agencies and
oDecorative fountains and
oStream flow and wetland