Water covers more than 70% of the Earth’s surface. It can exist simultaneously as a gas, a liquid and a solid on our planets.

When scientists look for evidence of life on other planets, one of the things they look for is water. This is because water is essential for life as we know it.   It is a very good solvent - some people call water the “universal solvent”, and  many of the substances found in  living organisms are dissolved in water.  Many metabolic processes use water.

Here are some science experiments that illustrate the properties of water.

Colors in a bottle

Why is water such a good solvent? Because of its polarity. A molecule of water contains two hydrogen atoms at one end and an oxygen atom at the other end. The end with the hydrogen atoms is slightly positive, while the end with the oxygen atom is slightly negative.

This property causes other polar molecules, such as salt and table sugar molecules, to be soluble in water.  When salt is added to water, salt molecules break up into positively charged sodium ions and a negatively charged chlorine ions; oppositely charged water molecules surround each ion.  When table sugar dissolves in water, the positive ends of the water molecules are attracted to the negative ends of sugar molecules, while the negative ends of water molecules are attracted to the positive ends of sugar molecules.

These substances dissolve in water because the forces of attraction between them and the water molecules are stronger than the forces that hold the water molecules together.

Not every substance dissolves in water, though.  With non-polar substances, such as oils and waxes, the bonds holding the water molecules together and the bonds holding the oil or wax molecules together are stronger than any bonds attracting the oil or wax to the water.

The following experiment shows how some substances dissolve in water while some do not.

Equipment Needed

Colored paraffin or melted candle wax
Colored ink
1 small bottle with a tight lid

The Experiment

Pour the colored paraffin and an equal amount of water into a small bottle.

Close the bottle tightly, and then shake it vigorously.

The water and paraffin will appear to mix at first.

However, as soon as put the bottle down, they will begin to separate from each other. Within a few seconds, the colored paraffin will be floating on top of the water. No matter how hard you shake the bottle you will never be able to make the two liquids mix.

Try this experiment with other liquids, such as glycerin.

Use colored inks to distinguish between them if they are of similar colors.

You can fill a bottle with layers of different colored fluids.

Filter with Capillary Action

Capillary action is the movement of a liquid through a narrow space, such as a narrow tube or the space between the fibers in a paper towel, in opposition to forces such as gravity.

It occurs because adhesive forces cause the liquid to stick to the sides of the material it is traveling through, while surface tension, which results from the tendency of water molecules to stick together, holds the surface of the water together.

Were it not for capillary action, nutrient-carrying water would not be able to travel from soil to the tops of tall trees.

This experiment will show you how you can use capillary action to create a simple filter.

Equipment Needed

2 bowls


Spoon for transporting the soil
Box or pile of books

1 candle wick

The Experiment

Stir two or three spoonfuls of soil into a bowl of water.

The soil will remain suspended in the water, discoloring it.

Place the bowl of dirty water on the box or pile of books.

Place the candlewick in the water and let the wick hang over one side so that it hangs down into the second bowl.

After a time, drops of clear water will fall from the free end of the wick and into the lower bowl.

This happens because capillary action causes the water to move along the wick, leaving the soil behind.

Changing the density of water

The Dead Sea, which borders Israel, Jordan and the West Bank, is a well-known tourist attraction.  Tourists especially like to experience the incredible buoyancy that it provides.  It is very easy to float on the Dead Sea, but impossible to dive or sink.

This is because of the Dead Sea’s high level of salinity. The high concentration of salt increases the density of water.

In fact, the Dead Sea is the saltiest sea on Earth. It is so salty that nothing but microbes can live in it permanently.

One microorganism, known as Heliobacterium halobium, thrives on the Dead Sea’s high salt concentration.

Here is an experiment, on a much smaller scale, which will show you how adding salt to water increases the water's density.

Equipment Needed

1 egg
A pitcher of water

The Experiment

Place the egg in the pitcher of water.

The egg will sink to the bottom.

Remove the egg.

Pour some salt in the water - about an egg-cupful of salt for every cup of water - and stir it.

Replace the egg.

The egg will now float, now that you have increased the density of water by adding salt to it.

Lifting Ice with String

Adding salt to water lowers the water’s freezing point.

This is why people spread salt over icy sidewalks.

This experiment will show you how you can use a piece of string to lift a block of ice.

Equipment Needed

1 bowl filled with water
1 block of ice
1 piece of string about six or seven inches long

The Experiment

Float the block of ice in the water

Wet one end of the piece of string. Place it on top of the ice and sprinkle a spoonful of salt over it.

The salt will melt the ice over the string.

After a while, the ice will refreeze, trapping the string.

Gently pull on the string. The block of ice will rise up out of the water.

Water Expands When it Freezes

An unusual property of water is that it is denser as a liquid than as a solid. This is why icebergs float on top of water, and ice cubes will float in a glass of water.

These experiments will demonstrate how water expands when it turns into ice.

Equipment Needed

1 Plastic cup
A freezer

The Experiment

Fill the cup up to the brim with water.

Place the cup in the freezer and wait for all of the water to freeze.

The ice will come up much higher than the brim of the cup.

Alternate Experiment

The following experiment requires the outside temperature to remain below the freezing temperature of water overnight, so whether you can perform the experiment will depend on where you live and the time of year.

Equipment Needed

1 glass bottle with a very strong lid

The Experiment

Fill the bottle to the top with water, and then close the lid tightly.

Place the filled bottle outdoors and leave it overnight.

In the morning, the water in the bottle will have frozen and turned to ice.

The sides of the bottle will be cracked open. (Be careful of broken glass.)

This happens because the ice, being less dense, requires more space than the water that you originally poured into the bottle. It cannot expand upward because the lid is stopping it, so it expands sideways instead, cracking the glass.