Discuss briefly about water quality , nature of impurities and disinfection of water.
Answers
Water is the universal solvent and in nature, it is never totally pure. No matter how isolated it is
from sources of contamination, it will always have some chemicals. Gases or minerals in the air,
soil, or rock are dissolved by the water. Some dissolved materials give water its characteristic
taste, and “pure water” is generally considered to be flat and tasteless.
Minerals can cause hardness (calcium or magnesium), color (iron), contamination (arsenic), and
radioactivity (radium, radon) in the water. Humans can cause contamination through the
improper use of pesticides or fertilizers and through the disposal of waste. These impurities can
dissolve in the water, causing it to be contaminated.
Minerals and impurities are normally present in very small concentrations, and are measured in
parts per million (ppm) (how many parts of impurities in a million parts of water) or milligrams
per liter (mg/l). The terms are equivalent and are used interchangeably in water and wastewater.
Some contaminants can also be measured in parts per billion (ppb) or micrograms per liter (μg/l),
which are also essentially equivalent.
Groundwater dissolves much of the material that it percolates through. It is generally harder than
surface water, and it usually contains more iron and manganese. As stated earlier, water in nature
is not pure. The table below shows typical concentration ranges for chemicals dissolved in
ground or surface water.
CONCENTRATIONS FOUND
IN GROUND WATER
CONCENTRATIONS
FOUND IN SURFACE
WATER
Total Hardness 300 - 400 ppm 75 - 200 ppm
Alkalinity 250 - 350 ppm 45 - 250 ppm
Dissolved Oxygen near 0 2 - 14 ppm
Carbon Dioxide 1 - 10 ppm low
Calcium Hardness high sometimes high, usually low
Magnesium Hardness tends to be high sometimes high, usually low
Water that exists in nature, like any other material, undergoes changes. These changes are driven
by both physical and chemical means. The quality of groundwater is generally slower to change,
especially when it comes from deeper aquifers. Groundwater is not directly exposed to air
pollution, contamination from run-off (if the well is properly constructed), or wastewater
discharge. The quality of groundwater is also protected by natural filtration, which can remove
some contaminants, as water percolates through the soils and rock.
Chemicals (either organic or inorganic) that dissolve in water can change its characteristics and
may cause it to become contaminated. Among other things, these chemicals could change its pH, cause hardness, or add dissolved oxygen.