Science of Water : Concepts and Applications

Environmental Biomonitoring, Sampling, and Testing 285
Over the years, several attempts to standardize the method of describing the “apparent” color
of water using comparisons to color standards have been made. Standard Methods recognizes the
visual comparison method as a reliable method of analyzing water from the distribution system.
One of the visual comparison methods is the Forel-Ule Color Scale, consisting of a dozen
shades ranging from deep blue to khaki green, typical of offshore and coastal bay waters. By using
established color standards, people in different areas can compare test results.
Another visual comparison method is the Borger Color System, which provides an inexpensive,
portable color reference for shades typically found in natural waters; it can also be used for its
original purpose—describing the colors of insects and larvae found in streams of lakes. The Borger
Color System also allows the recording of the color of algae and bacteria on streambeds.
√ Note: Do not leave color standard charts and comparators in direct sunlight.
Measured levels of color in water can serve as indicators for a number of conditions. For example,
transparent water with a low accumulation of dissolved minerals and particulate matter usually
appears blue, and indicates low productivity. Yellow to brown color normally indicates that the
water contains dissolved organic materials, humic substances from soil, peat, or decaying plant
material. Deeper yellow to reddish colors indicates some algae and dinofl agellates. A variety of
yellows, reds, browns, and grays are indicative of soil runoff.
√ Note: Color by itself has no health signifi cance in drinking waters. A secondary MCL is
set at 15 color units, and it is recommended that community supplies provide water that has
less color.
To ensure reliable and accurate descriptions of apparent color, use a system of color comparisons
that is reproducible and comparable to the systems used by other groups.
In treating for color in water, alum and ferric coagulation is often effective. It removes apparent
color and often much of the true color. Oxidation of color causing compounds to a noncolored
version is sometimes effective. Activated carbon treatment may adsorb some of the organics
causing color. For apparent color problems, fi ltration is usually effective in trapping the colored
particles.
Odor Analysis of Water
Odor is expected in wastewater—the fact is, any water containing waste, especially human waste,
has a detectable (expected) odor associated with it. Odor in a raw water source (for potable water)
is caused by a number of constituents. For example, chemicals that may come from municipal and
industrial waste discharges, or natural sources such as decomposing vegetable matter or microbial
activity may cause odor problems. Odor affects the acceptability of drinking water, the aesthetics of
recreation water, and the taste of aquatic foodstuffs.
The human nose can accurately detect a wide variety of smells and is the best odordetection
and testing device presently available. To measure odor, collect a sample in a largemouthed
jar. After waving off the air above the water sample with your hand, smell the sample.
Use the list of odors provided in Table 8.10—a system of qualitative description that helps
monitors describe and record detected odors to describe the smells. Record all observations. (See
Standard Methods.)
In treating for odor in water, removal depends upon the source of the odor. Some organic substances
that cause odor can be removed with powdered activated carbon. If the odor is of gaseous
origin, scrubbing (aeration) may remove it. Some odor-causing chemicals can be oxidized to odorless
chemicals with chlorine, potassium permanganate, or other oxidizers. Settling may remove
some material that when later dissolved in the water may have potential odor-causing capacity.
Unfortunately, the test for odor in water is subjective. There is no scientifi c means of measurement
and no method is very accurate.