Drinking Water Monitoring - The Drinking Water - page 219

• A burette is a long, graduated glass tube with a tapered tip like a
pipette and a valve that opens to allow the reagent to drip out of
the tube. The amount of reagent used is calculated by subtracting
the original volume in the burette from the column left after the
endpoint has been reached. Alkalinity is calculated based on the
amount used.
• Titrators forcefully expel the reagent by using a manual or mechani-
cal plunger. The amount of reagent used is calculated by subtracting
the original volume in the titrator from the volume left after the end-
point has been reached. Alkalinity is then calculated based on the
amount used or is read directly from the titrator.
• Digital titrators have counters that display numbers. A plunger is
forced into a cartridge containing the reagent by turning a knob on
the titrator. As the knob turns, the counter changes in proportion
to the amount of reagent used. Alkalinity is then calculated based
on the amount used. Digital titrators cost approximately $90. Digital
titrators and burettes allow for much more precision and uniformity
in the amount of titrant that is used.
Fecal Bacteria*
Members of two bacteria groups (coliforms and fecal streptococci) are used
as indicators of possible sewage contamination, because they are commonly
found in human and animal feces. Although they are generally not harmful
themselves, they indicate the possible presence of pathogenic (disease-caus-
ing) bacteria, viruses, and protozoans that also live in human and animal
digestive systems. Their presence in streams suggests that pathogenic micro-
organisms might also be present and that swimming in that water or eating
shellfish from that water might present a health risk. Because testing directly
for the presence of a large variety of pathogens is difficult, time consuming,
and expensive, water is usually tested for coliforms and fecal streptococci
instead. Sources of fecal contamination of surface waters include wastewater
treatment plants, on-site septic systems, domestic and wild animal manure,
and storm runoff. In addition to the possible health risk associated with
the presence of elevated levels of fecal bacteria, the bacteria can also cause
cloudy water, unpleasant odors, and an increased oxygen demand.
* Much of the information presented in the following sections is adapted from USEPA, Te st
Methods for Escherichia coli and Enterococci in Water by the Membrane Filter Procedure , EPA
600/4-85-076, Office of Research and Development, U.S. Environmental Protection Agency,
Cincinnati, OH, 1985; USEPA, Bacteriological Ambient Water Quality Criteria for Marine and
Fresh Recreational Waters , EPA 440/5-84-002, Office of Research and Development, U.S.
Environmental Protection Agency, Cincinnati, OH, 1986.