Water Quality and Common Problems
If we
think back to our school days, most of us can remember studying the
"hydrological cycle". You remember the process of how water vapor
condenses in the atmosphere and falls to earth as precipitation. Once on
the surface of the earth, most of the water evaporates back into the
atmosphere, where it will again condense and fall back to earth as
precipitation. About 30% of the precipitation, however, does not
evaporate. Instead, it seeps into the ground or runs off into streams,
rivers, or lakes. As the water seeps into the ground or as it flows over
the surface, it dissolves minerals and other substances contained in
the ground. Under the surface, the water tends to collect in porous
portions called 'aquifers.' These aquifers are the source of our well
water.
Points
To Keep In Mind
- Water as found in nature,
will always have some substances dissolved in it.
- It will always have the
potential to have particles suspended in it.
- It will always have the
potential to be a suitable home to disease causing organisms.
This
is true of "fresh" mountain streams, well water, and even municipally
treated water systems. To achieve "pure water", or anything close to
that goal, water must be filtered or treated in some way.
As
you begin to see, the problem for us to solve will depend upon what the
water has had contact with. These conditions can vary greatly, not only
from one region of the country to another, but also within the same
general location. Water drawn from wells in the same area may not be
exactly the same. The quality of water from a municipality owned
treatment facility will depend upon the age and condition of the
equipment. Even though the water may be classified as safe to drink, the
aesthetic quality may be less than desirable.
Fortunately,
our knowledge of the nature of water has increased steadily over the
years. The most frequently occurring problems have been studied very
closely. We now know the symptoms, the cause of the symptoms, and how to
cure the problem itself. Sometimes the symptoms are easy to read and
easy to cure. Other times, several problems exist in the water at the
same time. Then it gets more complicated, and usually more costly to
correct.
Let's examine these water problems as they will be
reported to you by your customers ... the symptoms they see, taste,
smell or fear. Along with the symptoms we will provide the cause of the
condition, so you will be able to explain to our customer exactly what
is going on with their water supply.
Common Water Problems
HARDNESS
(Calcium and Magnesium)
The term hardness refers to
the quantity of dissolved calcium and magnesium in water. These
minerals, which come primarily from limestone type rock formations, are
found to some degree in almost all natural waters. Calcium and magnesium
cause problems for two principal reasons:
- When the water is warmed, they precipitate out of solution and
form a hard, rock-like scale. This scale accelerates corrosion,
restricts flow, and reduces heat transfer in water heaters and boilers.
- When they combine with
soap, they react to form a curd, which interferes with cleaning, dries
out skin, and leaves deposits on plumbing and clothes (bathtub ring;
ring around the collar).
Waters which naturally
contain very little hardness can also be problematic because they may be
corrosive in some applications (such as acidity).
For
some applications, sequestering agents (Siliphos) are good for hardness
conditions under 15 gpg. The only practical method for hardness removal
above 15 gpg in residential applications is through cation exchange
process employed by water softeners (also called conditioners).
Acidity
(pH)
Water which contains excess acidity tends to act
aggressively towards plumbing and fixtures, causing corrosion and
staining (i.e.-blue green stains on fixtures from copper pipes).
Relative acidity/alkalinity is measured on the pH scale, ranging from 0-
1 4, where 7 is neutral, numbers lower than 7 are progressively more
acidic, and numbers higher than seven are increasingly alkaline (basic).
The pH value refers not to the quantity of acidity, but rather to the
relative acidity/alkalinity of a particular sample.
Alkalinity
acts as a buffer to deactivate the acidity, a process called
neutralization. For example, limestone (calcium carbonate) is often
applied to soil to offset the acidity which comes from acid rain and
decaying organic material. The acceptable range for water is 6.5-8.5.
Acidity
cannot be removed from water. However, it can be neutralized by raising
the pH with alkalinity. This can be done by injecting a highly basic
(alkaline) solution with a feed pump or by passing the water through a
bed of processed limestone or similar material.
Iron
(Fe)
The presence of Iron is a very common water quality
problem, particularly in water from deep wells. Water containing even a
significant quantity of iron may appear clear when drawn, but will
rapidly turn red upon exposure to air. This process is called oxidation,
and involves the conversion of ferrous (dissolved) iron, which is
highly soluble, to ferric (precipitated) iron, which is largely
insoluble. The ferric iron then causes red/brown staining on clothes,
fixtures, etc.
Iron concentration is measured in ppm or
mg/l (milligrams per liter, where 1 ppm = 1 mg/l). Staining usually
becomes a problem at concentrations greater than 0.3 ppm. Removal is
through ion exchange (water softener) or oxidation/filtration (APIR).
Manganese
(Mn)
Manganese is a metal similar to iron which causes a
grey/black stain. It can cause staining in concentrations as low as
0.05 ppm. Manganese is removed in a manner similar to iron, although
oxidation is more difficult, requiring a pH of at least 8.5.
Hydrogen
Sulphide (H2S)
Hydrogen Sulphide is a gas which smells
strongly like rotten eggs. It results from the decay of organic matter
with organic sulphur and the presence of certain types of bacteria. Even
very low concentrations are offensive as well as highly corrosive
(silver tarnishes almost immediately upon contact with H2S).
Because
it is in a gaseous form, H2S cannot be collected in a sample
bottle for laboratory analysis. Therefore, its presence must be
reported when a sample is submitted for a treatment recommendation. It
can be removed by oxidation/filtration, aeration, or well sanitization.
Turbidity
Turbidity
is a measure of suspended particles in water and can range from large
particles which settle out of solution rapidly (such as sand), to
extremely fine sediment which may stay suspended in solution even after
standing for hours. Treatment depends upon size, which is measured in
microns.
Tastes and Odors
Most tastes and odours are
caused by the presence of organic matter and chlorine. The vast
majority of these can be removed with activated carbon.
Organic
Chemical Contaminants
The presence of toxic chemicals at
various concentrations has been widely documented in many water
supplies. Detection can be difficult as these contaminants often have no
taste or odour. Treatment depends on type and concentration. These
chemicals may be industrial solvents or agricultural pesticides and
herbicides. One of the most common is Trihalomethane (THM) which is
formed when chlorine in the water reacts with natural organic matter.
Total
Dissolved Solids (TDS)
TDS is the sum of the mineral salts in
water and if too high can result in objectionable taste, cloudy ice,
interference with the flavor of foods and beverages and scale left
behind in cookware. Generally speaking, the lower the TDS the more
acceptable the drinking water. TDS of 1,000 ppm or more is unacceptable
for drinking water. Reverse Osmosis (R0) process has proven itself as
the most practical and cost effective method of correcting problems
caused by high TDS.
Nitrates (NO3)
Nitrates
are inorganic chemicals dissolved in some water supplies as a result of
feedlot and agricultural activities. Nitrate levels over 45 mg/L as
actual NO3 (or 10 mg/L as Nitrogen, N) can be a serious
health risk to infants and children. Reverse Osmosis has proven itself
as an effective method of reducing Nitrates to safe levels.
Heavy
Metals-Lead (Pb);Cadmium (Cd);Mercury (Hg);Arsenic (As);Selenium
(Se);Chromium (Cr)
The so-called heavy metals are toxic
elemental metals such as Lead, Cadmium, Mercury, and Arsenic that find
their way into water supplies from natural and industrial sources as
well as home plumbing. These metals, especially Lead, can seriously
affect the mental and neurological development of infants and children.
Reverse Osmosis (R0) is recognized as the most practical method of
reducing Lead to insignificant levels in drinking water. Carbon Block
technology that incorporates ceramic ion exchange media is also an
effective method of reducing lead.
Radium 226/228 (Ra)
Radium
occurs in ground water due to the radioactive decay of Uranium in
geologic formation. There is a health risk if the Radium level exceeds
20 pecocuries per liter (pCi/L). Cation exchange water softeners using
proper regeneration procedures are effective in reducing Radium for POE
applications. Reverse Osmosis systems are effective for reducing Radium
for POU applications.