45. Select Effective Water-treatment Methods
Taste. Odor. Hardness. Contamination. These are four of the most
common reasons why people install water-treatment systems in their
home. If you have a well and you identify excessive contaminant
levels in it, first pinpoint the source and try to correct the problem.
If correcting well deficiencies isn't the answer, consider a water-treatment
Make sure you know exactly which contaminants you want to get rid
of, as well as your financial limits. Consult with local officials
and water-treatment specialists at state agencies or universities.
And remember, each system does not work with equal efficiency on
all the contaminants it removes.
activated carbon filter removes many volatile organic chemicals, some
pesticides, radon gas, hydrogen sulfide, and mercury. It also reduces
odor, color, and taste problems (such as residual chlorine).
is filtered through carbon granules that trap contaminants. But infrequently
maintained filters can result in higher concentrations of contaminants
and can serve as a breeding ground for bacteria.
removes radium, odor, off-tastes, heavy metals, some pesticides, nitrate,
fluoride, and salt. Units with volatile gas vents can remove some
volatile organic chemicals as well.
distillation, water is evaporated, leaving impurities behind. The
steam is then cooled and becomes distilled water. But the distillation
process is slow and consumes a lot of energy, making it expensive.
It also consumes large amounts of water if the coolant used in the
distillation process is water. Distilled water can corrode materials
such as iron and copper in plumbing systems.
osmosis removes inorganic minerals such as radium, sulfate, calcium,
magnesium, potassium, nitrate, fluoride, boron, and phosphorous. It
also helps to remove salts, certain detergents, volatile organic contaminants,
some pesticides, and taste- and odor-producing chemicals.
is filtered through a membrane that has passages smaller than the
contaminant molecules. Under-the-sink installations are costly and
take up a lot of space. In addition, reverse osmosis is slow and wasteful
of water, and filter replacement is costly. Some microorganisms may
be small enough to pass through the reverse osmosis membrane and colonize
the holding tank.
or anion exchange (water softening) removes barium; radium; and taste,
color-, and odor-producing chemicals. It will remove dissolved iron
and manganese when they are present in low concentrations. Also, anion
exchange units will remove nitrate and fluoride, but cation exchange
units will not.
water softening process works by passing hard water through resin
beads. Magnesium and calcium ions in the water exchange places with
sodium ions on the beads, softening the water. People with hypertension
or high blood pressure should consult their doctor about personal
health risks associated with drinking softened water because of the
filtration removes dirt, sediment, loose scale, and insoluble iron
and manganese (flakes that have not dissolved). The water is cleared
by sand, filter paper, compressed glass wool, or other straining material.
Mechanical filtration does not do much to remove harmful, dissolved
removes bacteria; other microbiological contaminants; and some taste-,
odor-, and color-producing chemicals. Also, it removes hydrogen sulfide
and dissolved iron and manganese when followed by mechanical filtration
or an activated carbon filter.
chlorination, a pump feeds chlorine into the water. Chlorine has a
residual effect, which means it works for a while after being added
to the water. But if the system is not operated properly, it is expensive
and possibly toxic. Also, chlorination byproducts may be harmful.
radiation removes bacteria and other microbiological contaminants.
Water passes a special light bulb where ultraviolet radiation kills
contaminants. However, this system may not work effectively in cloudy
water or when the water flow is too fast. Also, unless the unit is
equipped with a special meter, it is hard to know whether the system
is doing the job. UV units do not have a residual effect, as chlorination
Ozonation removes bacteria; other microbiological contaminants; some
pesticides; and some taste-, odor-, and color-producing chemicals.
It also removes hydrogen sulfide and dissolved iron and manganese
when followed by mechanical filtration or an activated carbon filter.
With ozonation, water is exposed to ozone gas, which destroys microorganisms.
Equipment to generate ozone is expensive, and ozonation does not have
a residual effect, as chlorination does.
oxidizing filter (greensand filter or zeolite filter) removes iron,
manganese, and hydrogen sulfide. In addition, it removes some taste-,
odor-, and color-producing chemicals. Contaminants are removed through
filtering and chemical reactions. But the system needs to be regenerated
by pouring potassium permanganate into it. Potassium permanganate
can pose a hazard to eyes and skin during handling, so always wear