Potable Water

Potable water

water that is safe for humans to drink

Why is potable water not pure water?

it contains low levels of dissolved salts and microbes

What are the methods to produce potable water?

free water, salt water, distillation, reverse osmosis

Locations for the free water method

locations with lots of fresh/groundwater (e.g. UK)

Free water method - stage 1

choose an appropriate source of fresh water

Free water method - stage 2

-pass the water through filter beds
-low energy cost
-reason is to remove solid impurities from the water

Free water method - stage 3

-bubble chlorine or ozone though it
-low energy cost
-reason is to kill microorganisms (e.g. bacteria/viruses)

Locations for salt water methods

locations with limited fresh water supplies (e.g. Saudi Arabia)

Salt water method - stage 1

choose a salt water source

Salt water method - stage 2 (dn)

-distillation
-high energy cost
-reason is water evaporates, impurities stays & produces pure water

Salt water method - stage 2 (ro)

-reverse osmosis (using membranes)
-high energy cost
-reason is water is forced through a membrane at high pressure

Explain how distillation is used to purify salt water

-salt solution is heated
-water evaporates at 100 oC
-water vapour cools as it passes over the
reflux condenser and condenses back into
liquid water
-the salt remains in the round bottom flask

Explain how reverse osmosis is used to purify salt water

-water is passed into the system at high pressure.
-pure water passes through the semi-permeable
membrane whilst other ions and molecules in
the salt water cannot pass through.
-potable water is producted

Pure water

water that contains no other substances (only H2O)

What does potable water contain?

a range of ions (and microbes) but in low enough concentrations not to be harmful. i hmhx