Fresh water crisis and management
and Rain water Harvesting
Clean, fresh water is
essential for nearly every human activity. Perhaps more than any other
environmental factors, the availability of water determines the location and
activities of humans beings. Almost all agricultural operations which supply
food to humanity need water.
Freshwater
resources
Of the total water
available on earth, only 3% is fresh water.
1. Glaciers, ice and
snow : Of the 3 percent of all water that is fresh, about three – fourths is
tied up in glaciers, ice caps and snowfields. They occur only+ at high
altitudes or high latitudes.
2. Ground water :After
glaciers, the next largest reservoir of fresh water is held in the ground in
ground water. Water held in the lower soil layers is known as water table.
Porous- water bearing layers of sand, gravel and rock are called aquifers.
3. Lakes and Ponds :
Lakes are inland depressions that hold standing fresh water year around. Ponds
are small temporary or permanent bodies of shallow water. While lakes contain
nearly one hundred times as much water as all rivers and streams combined, they
are still a minor component of total world water supply.
4. Wet lands : Bogs,
swamps, wet meadows and marshes play a vital and often a minor role.
Freshwater
shortages
At least one billion
people or nearly 20 percent of the world’s population, lack safe drinking
water. The W.H.O. considers 53,000 gallons of good water per year to be the
minimum for a healthful life. Some forty countries (including island nations,
Middle East countries) in the world fall below this level.
Reasons
for freshwater shortages
1.
Natural forces
Deficits are caused by
natural forces such as poor rain fall and hot winds, rivers changing courses.
2.
Human causes
Include increased
population, rapid urbanization, over grazing by cattle, improper cultivation
methods, poor sewage systems, inadequate finances for providing infra
structures.
3.
Depleting ground water
Ground water is the
source of nearly 40 % water for agricultural and domestic use in most of the
countries. Nearly 95% of rural population depends on groundwater for drinking
and other domestic purposes. Over
use of the supplies
causes several kinds of problems, including drying of wells, natural springs
and disappearance of surface water features such as wetlands, rivers and lakes.
In many parts of the
world, groundwater is being withdrawn from aquifers faster than natural
recharge can replace it. On a local level this causes a level of depression in
the water table. A heavily pumped well can lower the ground water table so that
nearby shallower wells go dry. On a
broader scale, heavy pumping can deplete a whole aquifer. Many aquifers have
slow recharge rates, so it will take thousands of years to refill them once
they were emptied.
Depletion of ground water
Salt
water intrusion
Many parts of the world
are losing freshwater sources due to saltwater intrusion. Over use of under
ground freshwater reservoirs often allows salt water to intrude into aquifers
and affect the water table.
Fig. Salt water intrusion
5.
Loss of free flowing rivers
Loss of free flowing
rivers that are either drowned by reservoir impoundments or turned into linear,
sterile irrigation channels is yet another cause for freshwater crisis.
6. Evaporations,
leakage and siltation
It happens in
freshwater lakes, ponds and dams.
Freshwater
Management
On a human time scale,
the amount of water on the earth is fixed, for all practical purposes. There is
little we can do to make more water. However, there are several ways to
increase local supplies.
a)
Seeding clouds
Seeding clouds with dry
ice or potassium iodide particles sometimes can initiate rain if water laden
clouds and conditions that favour precipitation are present.
b)
Desalination
Desalination of ocean
water is a technology that have great potential for increasing fresh water. The
common methods of desalination are distillation (evaporation and
recondensation) or reverse osmosis (forcing water under pressure through a
semipremeable membrane whose tiny pores allow water to pass but exclude most
salts and minerals). Although desalination is still three to four times more
expensive than most other sources of freshwater, it provides a welcome water
supply in such places like Dubai, Oman and Bahrain where there is no other
access to fresh water.
c)
Dams, Reservoirs, Canals and Aqueducts
It is common to trap
run off with dams and storage reservoirs and transfer water from areas of
excess to areas of deficit using canals, tunnels and underground pipes.
d) Watershed management
A series of small dams
or tributary streams can hold back water before it becomes a great flood. Ponds
formed by these dams provide useful wildlife habitat and stock-watering
facilities. Small dams can be built with simple equipment and local labour,
eliminating the need for massive construction projects and huge dams.
e)
Rain water harvesting
The activity of
collecting rainwater directly or recharging it into ground to improve ground
water storage in the aquifer is called rain water harvesting. By rainwater
harvesting the ground water can be conserved, water table depletion can be
reduced and also sea water intrusion in coastal areas can be arrested. To
recharge the groundwater rainwater that falls in the terrace of the buildings
and in the open space around the buildings may be harvested. Roof top rain
water can be diverted to the existing open / bore well. Rainwater available in
the open spaces around the building may be recharged into the ground by the
following simple but effective methods.
The Government of
Tamilnadu leads the nation in implementing rain water harvesting programme. It
has made it mandatory for all houses and buildings in the State to install rain
water harvesting facility.
Rain
water harvesting f) Better agricultural
practices
Sound
farming and foresting practices can reduce runoff. Retaining crop residues on
fields reduces flooding. Minimizing ploughing and forest cutting on steep
slopes protects watersheds. Wetlands conservation preserves natural water
storage capacity and aquifer recharge zones.
g)
Domestic conservation
We could save as much
as half of the water we now use for domestic purposes without great sacrifice
or serious changes in our lifestyles. The use of washing machines, dish washers
and low volume shower heads can reduce water loss.
h)
Industrial conservation
Nearly half of all
industrial water use is for cooling of electric power plants and other
industrial facilities. By installing dry cooling systems, this could be
avoided. Cooling water can be recharged, some industrial wastewater may be
treated, recycled and reused.
i)
Saving water -an individual’s role
As an individual you
can conserve water by the following methods.
• Take shorter showers.
• Don’t wash car and two wheelers often
• Don’t allow tap run while washing
hands, dishes, food or brushing your teeth unnecessarily.
• In your lawn consider planting native
plants, a rock garden or some xerophytic landscaping.
• Use water conserving appliances : low
– flow showers and low -flush toilets.
• Use recycled water for lawns, house
plants and car washing
• Check taps for leaks
