potable water

potable water

water that is safe to drink

Low level of microbes

impure-has other dissolved substances

pure water

only h20

3 criteria for potable water

-pH 6.5-8.5

-no microorganisms

-low levels of dissolved substances

fresh water

water that contains insignificant amounts of salts, as in rivers and lakes

surface water sources

rivers, lakes, reservoirs

treating surface water

1)screening-remove large solid items

2)clarification-allow solid to settle to bottom

3)filtration-removes small particles suspended in water

4)chlorination-kills microorganisms in water

ground water sources

aquifers and ground water pumped to surface

how is ground water filtered

gravel beds

wastewater treatment to be returned to river

-screening-remove large solids

-sedimentation-allow solid to settle

-aeration-adding air and using biological treatment with bacteria. aeration provides oxygen needed by bacteria

-final settlement-allows remaining fine particles to settle before returned to river

test for chlorine

turns blue litmus paper red and white

aquifers

An underground water reservoir.

benefits of surface water

easy to access

replaced frequently by rain

cons to surface water

can dry up in hot weather

in warm areas , they rely on ground water

treating fresh water

1. collect freshwater (either rainfall or groundwater)

2. Wire mesh to screen out large twigs / objects

3. Gravel and sand bags filter out any solid bits

4. Sterilise water to kill microbes. Either by bubbling chlorine gas through it or using ozone or UV light

desalination

the removal of salt from seawater to make it usable for drinking and farming

desalination by distillation

-Sea water is heated until it boils.

-The salt remains in the liquid, and the steam is pure water.

-The steam is cooled and condensed to make potable water.

disadvantages of distillation

requires lots of energy

difficult to scale up at large quantities

waste water difficult to dispose off as very salty

Desalination by reverse osmosis

- water pushed by high pressure through membranes, salt left behind