Potable water

Potable water definition

Water that is safe to drink

Pure water definition

water that only contains H2O molecules

3 criteria for water to be considered potable

The levels of dissolved substances has to be fairly low, has to have a pH of between 6.5 - 8.5, there are no microorganisms in it.

How water collects on earth

Surface water and ground water

Surface water

Bodies of water that are exposed at their surface, e.g. lakes, rivers and reservoirs

Ground water

water sources found underground, like aquifers

Aquifers

Areas of permeable rock under the ground that trap water

Benefits of surface water

Easy to access, get replaced frequently by the rain

Disadvantage of surface water

They can dry up on a hot and sunny day

3 steps to make water potable

First take the fresh water and pass it through a wire mesh to filter out any big things like twigs, then pass it through a bed of sand and gravel, which filters out any other smaller bits. Finally, sterilise it to kill any microbes.

3 ways to sterilise water

Bubble chlorine gas through it, expose it to ozone/UV light

How countries without rain get potable water

Desalination

Desalination

Extracting potable water from seawater

2 methods of desalination

Distillation and reverse osmosis

How to desalinate through distillation

A larger version of simple distillation: evaporate the mixture and then condense it again to give pure distilled water

How to desalinate through reverse osmosis

The salty water is passed through a membrane which only allows water molecules to pass through. This means that all of the larger molecules get trapped and separated from the water, and so we end up with pure distilled water.