Transcript water_1_1_

Why do we have a limited supply of
water?
We have a limited supply
of water because 97% of
the water is salt water and
about 75% of the fresh
water is ice. Fresh water is
renewed through the water
cycle.
What causes water shortages?
Water shortages
happen when people
use water faster than it
is replaced. This is
most likely to happen
during a drought, which
is a period where less
rain than normal
comes.
Water Pollution
Water pollution is any
change to water that
can harm living
things. Some
pollutants just make
water unpleasant,
some can cause
sickness or death.
Most pollution is
caused by human
activities like sewage,
agricultural wastes,
industry and mining,
sediments, oil and
gasoline, and heat.
Sewage and Agricultural wastes
Sewage is human
wastes. When
untreated sewage
mixes with water, it can
make organisms very
ill. If treated sewage
mixes with water, the
bacteria in the water
will feed on it and
multiply, which takes
oxygen out of the
water. Animal waste,
pesticides, and
fertilizers can cause
pollution because the
rain can wash them
into the water.
Industry and Mining
Factories and mining
sites can release
chemicals and metal into
the water and make
organisms sick.
Sediments
Sediments are particles of
rock, silt, and sand.
Sediments cover up food
sources, nesting sites, and
eggs of organisms. They
also block the sun, which
makes underwater plants
not able to grow.
Oil and Gasoline
Oil spills are one of the
most dramatic forms of
water pollution. It can
cause organisms to die
from swallowing it. Birds
can get it in their
feathers and not be able
to fly. Gasoline can leak
out of storage tanks
underground and pollute
the groundwater.
Heat
Some factories release
water that was used to
cool hot machinery. This
heated water can cause
the temperature of the
water to change, which
kills the organisms.