Geoscience Reference
In-Depth Information
14.1.2.7 Water Constituents
Natural water can contain a number of substances known as impurities or constituents. When a
particular constituent can affect the good health of the water user, it is called a contaminant or pol-
lutant . It is these contaminants that the environmental practitioner works to keep from entering or
to remove from the water supply.
14.1.2.7.1 Solids
Other than gases, all contaminants of water contribute to the solids content. Natural water car-
ries many dissolved and undissolved solids. The undissolved solids are nonpolar substances and
consist of relatively large particles of materials, such as silt, that will not dissolve. Classified by
their size and state, by their chemical characteristics, and by their size distribution, solids can be
dispersed in water in both suspended and dissolved forms. The size classifications for solids in
water are
• Suspended solids
• Settleable solids
• Colloidal solids
• Dissolved solids
Total solids are the suspended and dissolved solids that remain behind when the water is removed
by evaporation. Solids are also characterized as being volatile or nonvolatile .
Key Point: Though not technically accurate from a chemical point of view because some finely sus-
pended material can actually pass through the filter, suspended solids are defined as those that can
be filtered out in the suspended solids laboratory test. The material that passes through the filter is
defined as dissolved solids. Colloidal solids are extremely fine suspended solids (particles) less than
1 micron in diameter; they are so small (though they still can make water cloudy) that they will not
settle even if allowed to sit quietly for days or weeks.
14.1.2.7.2 Turbidity
Simply, turbidity refers to how clear the water is. The clarity of water is one of the first charac-
teristics people notice. Turbidity in water is caused by the presence of suspended matter, which
results in the scattering and absorption of light rays. The greater the amount of total suspended
solids (TSS) in the water, the murkier it appears and the higher the measured turbidity. Thus, in
plain English, turbidity is a measure of the light-transmitting properties of water. Natural water
that is very clear (low turbidity) allows us to see images at considerable depths. High turbidity
water, on the other hand, appears cloudy. Keep in mind that water of low turbidity is not necessar-
ily without dissolved solids. Dissolved solids do not cause light to be scattered or absorbed; thus,
the water looks clear. High turbidity causes problems for the waterworks operator, as components
that cause high turbidity can cause taste and odor problems and will reduce the effectiveness of
disinfection.
14.1.2.7.3 Color
Water can be colored, but often the color of water can be deceiving. In the first place, color is
considered an aesthetic quality of water with no direct health impact. Second, many of the colors
associated with water are not true colors but the result of colloidal suspension and are referred to
as the apparent color . This apparent color can often be attributed to iron and to dissolved tannin
extracted from decaying plant material. Tr ue color is the result of dissolved chemicals (most often
organics) that cannot be seen.
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