Environmental Engineering Reference
In-Depth Information
The two basic methods for analyzing water samples for bacteria in com-
mon use are the membrane filtration and multiple-tube fermentation meth-
ods. Given the complexity of the analysis procedures and the equipment
required, field analysis of bacteria is not recommended. Bacteria can either
be analyzed at a well-equipped lab or sent to a state-certified lab for analysis.
If a bacteria sample is sent to a private lab, make sure that the lab is certified
by the state for bacteria analysis. Consider state water quality labs, university
and college labs, private labs, wastewater treatment plant labs, and hospi-
tals. This text does not address laboratory methods, because several bacteria
types are commonly monitored and the methods are different for each type.
For more information on laboratory methods, consult the latest edition of
Standard Methods
.
Note:
If you decide to analyze your samples in your own lab, be sure to
carry out a quality assurance/quality control program.
Apparent Color
Some aspects of water quality can be judged by its color. Noticeable color is
an objectionable characteristic that makes the water psychologically unac-
ceptable to the consumer (De Zuane, 1997). Pure water is colorless, but water
in nature is often colored by foreign substances. The color in water that is
partly due to dissolved solids that remain after removal of suspended matter
is known as
true color
.
Apparent color
(the topic of this section) results from
dissolved substances and suspended matter and provides useful informa-
tion about the source and content of the water. Simply stated, when turbidity
is present, so is apparent color. Natural metallic ions, plankton, algae, indus-
trial pollution, and plant pigments from humus and peat may all produce
color in water. Pure water absorbs different wavelengths (colors) of light at
different rates. Blue and blue-green light are the wavelengths best transmit-
ted through water, so a white surface under “colorless” water looks blue (e.g.,
Caribbean and some South Pacific Island waters above white sand).
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 dif-
ferent areas can compare test results. Another visual comparison method
is the Borger Color System, which provides an inexpensive, portable color
