Good Water Quality Chemical Parameters
What
Are The Chemical Parameters Of Good Water Quality?
Alkalinity is one
of the first considerations when it comes to the chemical quality of a source
water.
Alkalinity is not
a pollutant. It is a total measure of the substances in water that have
"acid-neutralizing" ability.
Don't confuse
alkalinity with pH.
pH measures the
strength of an acid or base; alkalinity indicates a solution's power to react with
acid and "buffer" its pH - that is, the power to keep its pH from
changing.
To illustrate, we
will compare two samples of pure water and buffered water.
Absolutely pure
water has a pH of exactly 7.0. It contains no acids, no bases, and no (zero)
alkalinity.
The buffered
water, with a pH of 6.0, can have high alkalinity. If you add a small amount of
weak acid to both water samples, the pH of the pure water will change instantly
(become more acid).
But the buffered
water's pH won't change easily because the Alka-Seltzer-like buffers absorb the
acid and keep it from "expressing itself."
Alkalinity is
important for fish and aquatic life because it protects or buffers against pH
changes (keeps the pH fairly constant) and makes water less vulnerable to acidrain.
The main sources
of natural alkalinity are rocks, which contain carbonate, bicarbonate, and
hydroxide compounds. Borates, silicates, and phosphates may also contribute to
alkalinity.
Limestone is rich
in carbonates, so waters flowing through limestone regions generally high
alkalinity - hence its good buffering capacity.
Conversely,
granite does not have minerals that contribute to alkalinity. Therefore, areas
rich in granite have low alkalinity and poor buffering capacity.
Chlorine is a
greenish-yellow gas that dissolves easily in water. It has a pungent, noxious
odor that some people can smell at concentrations above 0.3 parts per million.
Because chlorine
is an excellent disinfectant, it is commonly added to most drinking watersupplies in the US.
In parts of the
world where chlorine is not added to drinking water, thousands of people die
each day from waterborne diseases like typhoid and cholera.
Chlorine is also
used as a disinfectant in wastewater treatment plants and swimming pools. It is
widely used as a bleaching agent in textile factories and paper mills, and it's
an important ingredient in many laundry bleaches.
Free chlorine
(chlorine gas dissolved in water) is toxic to fish and aquatic organisms, even
in very small amounts.
However, its
dangers are relatively short-lived compared to the dangers of most other highly
poisonous substances.
That is becausechlorine reacts quickly with other substances in water (and forms combined
chlorine) or dissipates as a gas into the atmosphere.
The free chlorine
test measures only the amount of free or dissolved chlorine in water. The total
chlorine test measures both free and combined forms of chlorine.
If water contains
a lot of decaying materials, free chlorine can combine with them to form
compounds called trihalomethanes or THMs.
Some THMs in high
concentrations are carcinogenic to people. Unlike free chlorine, THMs are
persistent and can pose a health threat to living things for a long time.
People who are
adding chlorine to water for disinfection must be careful for two reasons:
1.
Chlorine gas even at low concentrations can irritate eyes, nasal passages and
lungs; it can even kill in a few breaths; and
2.
The formation of THM compounds must be minimized because of the long-term
health effects. Less than one-half (0.5) mg/L of free chlorine is needed to
kill bacteria without causing water to smell or taste unpleasant.
Most people can't
detect the presence of chlorine in water at double (1.0 mg/L) that amount.
Although 1.0 mg/L chlorine is not harmful to people, it does cause problems for
fish if they are exposed to it over a long period of time.
Nitrite and
Nitrate are forms of the element Nitrogen, which makes up about 80 percent of
the air we breathe. As an essential component of life, nitrogen is recycled
continually by plants and animals, and is found in the cells of all living
things.
Organic nitrogen
(nitrogen combined with carbon) is found in proteins and other compounds.
Inorganic nitrogen may exist in the free state as a gas, as ammonia (when
combined with hydrogen), or as nitrite or nitrate (when combined with oxygen).
Nitrites and
nitrates are produced naturally as part of the nitrogen cycle, when a bacteria
'production line' breaks down toxic ammonia wastes first into nitrite, and then
into nitrate.
Sources of nitrites
and nitrates
Nitrites
are relatively short-lived because they're quickly converted to nitrates by
bacteria. Nitrites produce a serious illness (brown blood disease) in fish,
even though they don't exist for very long in the environment.
Nitrites also
react directly with hemoglobin in human blood to produce methemoglobin, which
destroys the ability of blood cells to transport oxygen.
This condition is
especially serious in babies under three months of age as it causes a condition
known as methemoglobinemia or "blue baby" disease.
Water with nitrite
levels exceeding 1.0 mg/L should not be given to babies.
Nitrite
concentrations in drinking water seldom exceed 0.1 mg/L.
Nitrate is a major
ingredient of farm fertilizer and is necessary for crop production. When it
rains, varying nitrate amounts wash from farmland into nearby waterways.
Nitrates also get
into waterways from lawn fertilizer run-off, leaking septic tanks and
cesspools, manure from farm livestock, animal wastes (including fish and
birds), and discharges from car exhausts.
Nitrates stimulate
the growth of plankton and waterweeds that provide food for fish. This may
increase the fish population.
However, if algae
grow too wildly, oxygen levels will be reduced and fish will die.
Nitrates can be
reduced to toxic nitrites in the human intestine, and many babies have been
seriously poisoned by well water containing high levels of nitrate-nitrogen.
The U.S. Public
Health Service has established 10 mg/L of nitrate-nitrogen as the maximum contaminationlevel allowed in public drinking water.
Effects of
nitrates and nitrites on fish and aquatic life Nitrate-nitrogen levels below 90
mg/L and nitrite levels below 0.5 mg/L seem to have no effect on warm-water
fish*, but salmon and other cold-water fish are more sensitive.
The recommended
nitrite minimum for salmon is 0.06 mg/L. Dissolved oxygen (DO, pronounced
dee-oh) is oxygen that is dissolved in water.
It gets there by
diffusion from the surrounding air; aeration of water that has tumbled over
falls and rapids; and as a waste product of photosynthesis.
Fish and aquatic
animals cannot split oxygen from water (H2O) or other oxygen-containing
compounds. Only green plants and some bacteria can do that through
photosynthesis and similar processes.
Virtually all the
oxygen we breathe is manufactured by green plants. A total of three-fourths of
the earth's oxygen supply is produced by phytoplankton in the oceans.
If water is too
warm, there may not be enough oxygen in it. When there are too many bacteria or
aquatic animal in the area, they may overpopulate, using DO in great amounts.
Oxygen levels also
can be reduced through over fertilization of water plants by run-off from farm
fields containing phosphates and nitrates (the ingredients in fertilizers).
Under these
conditions, the numbers and size of water plants increase a great deal. Then,
if the weather becomes cloudy for several days, respiring plants will use much
of the available DO.
When these plants
die, they become food for bacteria, which in turn multiply and use large
amounts of oxygen.
How much DO an
aquatic organism needs depends upon its species, its physical state, water
temperature, pollutants present, and more.
Consequently, it's
impossible to accurately predict minimum DO levels for specific fish and
aquatic animals.
For example, at 5
C (41 F), trout use about 50-60 milligrams (mg) of oxygen per hour; at 25 C (77
F), they may need five or six times that amount.
Fish are
cold-blooded animals, so they use more oxygen at higher temperatures when their
metabolic rate increases.
http://www.freedrinkingwater.com/water_quality/quality1/1-chemical-parameters-good-water-quality.htm
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RELATED POSTS:
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Alkaline Water
Types of Water
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Alkaline Water
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Physical Parameters
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Types of Water
BASIC TYPES OF WATER DEFINED
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CLICK HERE . . .
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