Environmental Microbiology of Aquatic and Waste Systems

8 1 Nature, Properties, and Distribution of Water

1.2.3 Irrigation and Aquaculture

Throughout the world, irrigation for growing crops is
probably the most important use of water (except for
drinking). Almost 60% of all the world’s freshwater
withdrawals goes towards irrigation uses. Large-scale
farming cannot provide food for the world’s large pop-
ulations without the irrigation of crop fields by water
from rivers, lakes, reservoirs, and wells. Without irri-
gation, crops could never be grown in the deserts of
countries such as California and Israel.
Another agricultural use to which water is put is in
aquaculture for growing fish.

1.2.4 Power Generation

Power generation with water is in two forms:
Hydroelectric and thermoelectric.

1. Hydroelectric power contributes about 12% of total
   power output in the USA. This kind of power
   generation is restricted to regions where water can
   fall from a high altitude, and in the process cause
   the rotation of huge turbines which leads to the
   generation of electric power.


2. Thermoelectric production of electrical power
   results in one of the largest uses of water in the
   United States and worldwide. In thermoelectric
   power generation, water is heated either by petro-
   leum oil or gas or by heat generated in a nuclear
   reaction. The steam produced is used to drive
   turbines which generate the electricity. In the
   USA, in the year 2000, about 195,000 million
   gallons of water each day were used to produce
   electricity (excluding hydroelectric power). This
   represented about 52% of fresh surface-water
   withdrawals.

1.2.5 Transportation

Water is a primary medium for transporting heavy
goods. Huge ships ply the oceans and large lakes of
the world, carrying raw materials and manufactured
pro ducts. Water transportation, although relatively
slow is one of the cheapest means of transporting
heavy goods.

1.2.6 Recreation

Water is used for many recreational purposes, as well

as for exercising and for sports. Some of these include

swimming, waterskiing, boating, fishing, and diving.

In addition, some sports, like ice hockey and ice skating,

take place on ice.

1.2.7 Human Affairs

Water has played an important part in human affairs

for centuries, and still does (Keeley 2005 ).

1. Religion: Water is considered a purifier in most
   religions. Major faiths that incorporate ritual
   washing (ablution) include Hinduism, Christianity,
   Islam, Judaism, and Shinto. Water baptism is a
   central sacrament of Christianity; it is also a part
   of the practice of other religions, including Judaism
   and Sikhism. In addition, a ritual bath in pure
   water is performed for the dead in many religions
   including Judaism and Islam.
   Many religions also consider particular bodies
   of water to be sacred or at least auspicious, for
   example, the River Ganges in Hinduism.
   Greek philosophers believed that water was one
   of the four classical elements along with fire, earth,
   and air. Water was also one of the five elements in
   traditional Chinese philosophy, along with earth, fire,
   wood, and metal. Among the Igbos in Nigeria, water
   and rainfall are considered blessings; rainfall during
   a celebration is considered a good omen.


2. Politics: Water has caused frictions and even wars
   between nations: for example, the Ganges is dis-
   puted between India and Bangladesh, while the
   Golan Heights which provides 770 million cubic
   meters of water per year is disputed between Israel
   and Syria.

1.3 The Hydrologic Cycle

The continuous circulation of water from the earth to

the atmosphere and from the atmosphere back to the

earth is known as the hydrologic cycle. The hydrologic

cycle is powered by the energy of the sun. The cycle

operates through evaporation, transpiration in plants,

condensation in clouds, and precipitation.