Clean Water Science

evaporating and condensing Water must surely be one of our most precious resources.  Keeping up a supply of clean, fresh water is hard work and in many parts of the world people cannot take safe drinking water for granted.  All the water available to us is continually recycled – you could be drinking the same water as Julius Caesar and Cleopatra!  We refer to this process as the water cycle.  But what can we do to make sure the water we use is safe?  Here are some really great ideas and activities for a science fair project based on purifying water. 

Make A Solar Powered Water Still:

This is a super way of purifying water, you will need the following materials:

  • A large, glass bowl
  • A glass that will sit comfortably within the bowl.
  • Cling-film
  • A stone
  • Water
  • Salt, food dye, glitter, mud – you can be a little creative here, these are your water contaminants!

What to do:

Fill your bowl to about a third of its volume with water.  Place your glass in the middle.  Its rim should be higher than the water level but at least a centimetre lower than the rim of the bowl. 

Contaminate your water, you can add food dye, salt, glitter, whole spices – anything to make the water a bit yucky!

Now cover the top of your bowl tightly with cling-film. Don’t leave any gaps for water vapour to escape through.

Position a stone on top of the cling film directly above the glass.  There should be a gap in between the cling film and the top of the glass.  If there isn’t either use a smaller stone or see if you can stretch the cling film to lift the stone a litte.

Leave your bowl on a really warm and sunny windowsill.  Watch and observe what happens over the next week or so.


What happened here?

As the temperature inside the bowl begins to warm up, water evaporates and rises as water vapour.  When the vapour comes into contact with the cling film it begins to cool down again.  This causes the water condense and drops of water gradually form.  As the drops grow larger they run together and then run down the cling-film to the centre of the bowl under the stone where it drops into the glass as pure, clear water!

This method of cleaning water, or distillation to give it the proper name, is used on a larger scale in many hot countries where fresh water is scarce.  Salt is removed from seawater in this way to make it usable.  The process is called desalination.

In cooler climates where fresh water is more plentiful it is more common to treat water by filtering it and by adding various chemicals to purify and disinfect the water so that it is absolutely safe for you to drink.  

Ancient Egyptians treated water by siphoning water out of the top of huge jars after allowing the muddy water from the Nile River to settle at the bottom, in modern treatment plants a similar process is used call flocculation.  Chemicals are added to make the particles of sediment in the water cling together, this forms a dense layer of debris called floc which then sinks to the bottom of tanks. 

Boiling will kill a lot of the bacteria in water, but you can’t guarantee it will kill all of it!  

Try Making Your Own Water Filter:

For this you will need:

  • A clear 2L plastic bottle
  • Stones
  • Gravel
  • Sand
  • Vermiculite (from the potting shed or garden centres!)
  • Porous cloth such as crepe, net, muslin.
  • Elastic band
  • A jug of water made dirty with stones, soil and weeds from the garden!
  • A bowl for catching your filtrate.
  • Two pairs of hands are very useful here!

What to do:

Remove the bottle cap and cover the neck of the bottle with your muslin and secure it with a rubber band.

Carefully cut away the bottom of the bottle.

Now make your layers, each should be at least 5cms thick.  Start with the vermiculite, then add the sand, followed by gravel and finally the stone layer.

Place a clear bowl under your filter and then pour the dirty water in.

How much cleaner was the resulting water or filtrate? Did different layers of your filter catch different types of contaminant?

Putting water into to context – Water Facts:

  • 97 % of earth’s water is in the oceans. Only 3 % of the earth’s water can be used as drinking water.
  • 75 % of the world’s fresh water is frozen in the polar ice caps.
  • Water scarcity affects one in three people on every continent of the globe.*
  • Water scarcity forces people to rely on unsafe sources of drinking water. It also means they cannot bathe or clean their clothes or homes properly.
  • Every 20 seconds, a child dies from a water-related disease. 
  • Although a person can live without food for more than a month, a person can only live without water for approximately one week.

*Find out more here at the World Health Organisation (WHO).

What has been learned?

Knowledge base:

  • Solids can be separated from liquids by filtering.
  • Liquids can be distilled using evaporation and condensation.
  • That water evaporates when warm, and condenses when cooled.
  • The importance of  clean water in everyday contexts.

Take if further:

Find out more about the properties of water in our Water Density Experiment and Exploring Surface Tension.

{ 7 comments… read them below or add one }

Stephanie - Green Stay at Home Mom April 6, 2011 at 6:01 pm

Sounds like quite a project. My kids would probably love it though, but I think my youngest would really add to the challenge. She’s two and would probably knock the whole thing over if we weren’t careful, and possibly even if we were. She’s pretty much into everything right now.

Just need a couple sunny days here. We’re in southern California, and about to get some rain.
Stephanie – Green Stay at Home Mom recently posted..How Viable Is Solar PowerMy ComLuv Profile


Mandy April 7, 2011 at 7:58 am

Hi Stephanie, yes I think this is one to save for when your daughter is a little older, we do have lots of lovely toddler and baby activities – more on the way – which might be more appropriate and which I’m sure she’d enjoy. It makes me feel a bit better about our grey weather knowing that it actually does rain in California!


Marina at My Busy Children April 8, 2011 at 3:56 pm

I think we often underestimate the importance of water quality and cleanliness. Since we use water for everything, it is really impostant to purify it and get kids on board with projects like that
Marina at My Busy Children recently posted..Organic Chocolate GiveawayMy ComLuv Profile


zoe rivas November 13, 2011 at 1:12 am



Mandy November 13, 2011 at 9:19 am

Thanks Zoe, we wish you the best of luck with your science project!


Nikenya July 6, 2012 at 6:10 am

Nice information, is real science, i like it, will like to try this project. thamnks soo much for all.


Mandy July 13, 2012 at 1:11 pm

Thanks for stopping by Nikenya, hope your project is a success!


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