C3bL1 Water

Key Words

Disinfect - get rid of micro-organisms

Distillation - a liquid is boiled off, then made to cool against a cold surface, giving a very pure liquid.

Fluoridation - addition of sodium fluoride to drinking water.

Micro-organisms - bacteria, viruses, and tiny little animals.

Purify - make water cleaner than clean.

Water Cycle - cycling of water from the oceans to fall as rain, flow down rivers and back into the oceans again.

Grade E

Most of the Earth's surface is covered with water.  Most of the water is locked up in the sea, or in glaciers. Some evaporates, condenses into clouds which dump rain on the land.  The water flows into rivers, until it ends up in the sea again.  A tiny proportion is used for us to wash, drink, and use for industry.  Much of that goes back into the rivers, although a small proportion goes back into the air as water vapour.

We need water, but it must be pure.  If it has too many micro-organisms, it can make us ill.  We also need to clean it after we have used it.  Rivers awash with lavatory waste are really quite offensive, and hazardous to health.  Some rivers are badly polluted with industrial waste.

Water sources need to be kept well away from polluted areas.  Reservoirs are often in the remote hills and water is brought to the cities in aqueducts.

Grade C

The water cycle is summed up in this picture:

Water is purified by passing it over filters of sand and activated charcoal.  This process gets rid of most of the unpleasant material that is in the water.  The water is stored in underground reservoirs, then drawn off into the pipes.  The water has chlorine added to disinfect the water by killing off any micro-organisms, like bacteria, and protozoa (little animals).

In some very dry countries, water is pumped from the sea to be distilled.  Sea water is boiled, and the vapour cooled in a condenser.  The result is very pure water.  Desalination plants take a lot of fuel, so it's only economical if there is a plentiful supply of cheap fuel.

Grade A/A*

Sodium fluoride is sometimes added to water to help to improve the dental health of people in the area.  Too much fluoridation may make teeth mottled.  The treatment is controversial, since everyone has to take it with water, without choice.  People who are for fluoridation say that the benefits outweigh the risks.