Environmental Engineering Reference
In-Depth Information
Color
The quality of water can also be judged by its color, and the consumer does
so, at least from a psychological point of view. Imagine going to the kitchen
tap and drawing a glass of water that is rust colored, maybe to the point
where you cannot even see your fingers on the other side of the glass. The
rust-colored water may be safe to drink, but do you honestly think that the
average consumer—who is used to drinking a colorless glass of water—is
going to happily consume the rust-colored contents of that glass? Doubtful,
at best.
Pure water is colorless, but water in nature is often colored by foreign
substances, including organic matter from soils, vegetation, minerals, and
aquatic organisms that are often present in natural waters. Color can also be
contributed by municipal and industrial wastes. Color in water is classified
as either true color or apparent color. Color partly due to dissolved solids that
remain after removal of suspended matter is known as true color; color con-
tributed by suspended matter is called apparent color. In water treatment,
true color is the most difficult to remove. Color in water, although not usually
considered unsafe or unsanitary, does present a treatment problem because
it exerts a chlorine demand, which reduces the effectiveness of chlorine as a
disinfectant. Color is measured by comparing the water sample with stan-
dard color solutions or colored glass disks. One color unit (CU) is equivalent
to the color produced by a 1-mg/L solution of platinum. In 1989, the USEPA
issued a secondary MCL of 15 color units for color. At 10 to 15 color units,
color may not be visually detectable; at 100 color units, water may have the
appearance of tea.
Note:
In practice, the process of isolating and identifying specific chemi-
cals that cause the color is not practical.
As we have pointed out, color in water is a matter of aesthetics; consum-
ers do not find it acceptable. No matter how safe the water may be to drink,
most people object strongly to water that offends their sense of sight. Given a
choice, the public obviously would prefer clear, uncolored water. The effects
of color in water, though, extend beyond psychological implications; for
example, colored water affects laundering, papermaking, manufacturing,
textiles, and food processing. The color of water has a profound effect on its
marketability for both domestic and industrial use.
DID YoU KNoW?
1 million gallons = 3069 acre-feet = 133,685.64 cubic feet
