Water properties as a liquid

On earth most of the water exists in its liquid state as salty water in the oceans with lesser quantities of fresh water in lakes, rivers and clouds. For water to exist as a liquid, the temperature must be between 0°C and 100°C.

Note that water was used as the baseline for the Celsius scale: 0°C is the temperature at which water freezes and 100°C is the level at which water boils (at sea level).  Pure water is colourless, odourless and tasteless. The blue ocean colour you see is actually reflections from the sky.

Water has a very high surface tension. In other words it is elastic and sticky and tends to clump together in drops rather than spread out in a thin film. Surface tension is responsible for capillary action and this allows water (and its dissolved substances) to move through the roots of plants and through the tiny blood vessels in our bodies.

Water properties as a gas
 

Water as a gas is colourless and odourless. A fog you might see on a cold morning or the vapour above boiling water is a mist of liquid droplets. Steam is the invisible gas which is just on top of boiling water and below the visible mist. Pure steam exists at temperatures above 100°C.

Condensation is when water forms on the outside of a cold glass or on the inside of a window in winter.   Condensation forms from water vapour in the air and in cold air, water vapour condenses faster than it evaporates. As a result, when warm air touches the outside of a cold glass the air next to the glass becomes chilled and some of the water in that air turns from water vapour to tiny liquid water droplets.  Rain is produced by water vapour evaporating from the earth which then condenses in the sky

Other water properties
 

Water can carry dissolved materials along with its flow and it can act as a cleanser and dilute many wastes. Because water is so good at dissolving substances pure water is rarely found in nature. Streams and lakes can often look green or brown because of the mud or sand that has been dissolved in the water

Because water can store a large amount of heat without a big change in its temperature, large bodies of water like lakes change temperature slowly.  Creatures and plants that live in the water are then protected from rapid temperature changes.

It also takes large amounts of heat to make air evaporate or turn to vapour. When a water particle gains enough heat to be released from the other water molecules in liquid water, evaporation occurs. Liquid water changes temperature very slowly.

The hottest water molecules move fast enough so that they escape from the other water molecules. As evaporation has a cooling effect the water molecules which are left behind are usually slower moving, cooler molecules. Water helps to even out the Earth's climate a little.

Because water is such an effective cooler, it is used as a coolant in things like car radiators. It takes almost nine times as much heat energy to increase the temperature of water by 1°C than it does to increase the temperature of the same weight of sand by 1°C.

Water and the human body

Without water we would not be able to live. It makes up two-thirds of our body and we use it in so many ways: for drinking, watering, gardening, washing, for removing our wastes and for recreational activities.

A person can live approx one month without food but only about a week without water. As water is the main ingredient in the fluids within your body it is one of the most important nutrients you need.

It might not seem like it but water is one of the most necessary nutrients of all with your eyes and intestines needing water-based fluids to survive. Water cools our bodies, lubricates it, carries nutrients through it and removes our wastes. Our blood is made up of around 85 per cent water and 75 per cent of the weight of our brain is water.