Water seems to be everywhere in New Zealand. Oceans surround us. There are hundreds of lakes and rivers. Some South Island regions get more than 10 metres of rain each year. We have so much water, it’s easy to forget how important and unusual water really is.
Water is important
Water covers nearly three-quarters of the Earth’s surface. It is found on the land, under the ground and in the atmosphere. Water can be fresh (as in lakes, rivers or underground aquifers), brackish (as in estuaries) or salty (like in the oceans). Fish, other animals and plants live in water.
Plants and animals that live on land also need water. The human body is up to 78% water, and we need to keep our bodies hydrated by drinking water when we feel thirsty.
Water affects how our Earth works and looks. Water in the mantle (the layer between Earth’s crust and the core) influences the formation of volcanoes. Weather patterns are affected by water in the oceans, on land and in the air. Water – in the form of rain, rivers or glaciers – helps to shape our land.
Humans rely on water. We use it for fun – swimming, boating and other types of recreation. We use it for transport – ships carry people and goods all over the world. We use water to generate electricity.
One important way we use water is to grow our food. We use it to grow fruit, vegetables and grass for cows. Water is also needed to process food. For example, it takes about:
- 1000 L of water to produce 1 L of milk
- 500 L to produce 1 L of coffee
- 200 L to produce 1 L of Coca Cola
- 160 L to produce 1 banana
- 1700 L to produce a 100 g bar of chocolate.
Water has unusual characteristics
Water has some characteristics that make it an unusual substance.
Water is the only common substance that is naturally found as a solid (ice), liquid (water) or a gas (water vapour).
When water freezes into ice, it floats. This is because it is less dense than the surrounding water. This is different to most substances, where the solid state is denser than the liquid state. For example, a piece of solid candle wax will sink when placed in molten wax.
It is very important that ice floats. It means that the surface of rivers, lakes and other water bodies freeze from the top down. This allows animals and bottom-dwelling plants to survive in the water beneath the ice. Because ice floats, it stays at the surface and is exposed to the Sun and warm temperatures, and it melts.
Water dissolves things
Another unusual feature of water is that it can dissolve many things. Water is often called the universal solvent because more substances dissolve in water than in any other liquid. Not everything dissolves in water, though. Oils, waxes and fatty things like butter don’t.
Water has a thin elastic layer
Have you ever wondered why water droplets stick together to form a dome? Or why some insects can walk on water? The surface of water and other liquids acts like a thin elastic layer – scientists call it surface tension. Water is unusual because it has the greatest surface tension of any liquid at room temperature other than mercury.
Activity ideas
The Tip of the iceberg image shows how ice floats in salty seawater. Place an ice cube in a glass of water and observe if it floats in the same manner.
Looking at water – solid, liquid or gas provides a hands-on experience of water in its different states.
Explore water's surface tension further with these activities:
- Observing water’s thin skin – three simple activities demonstrate water’s thin elastic layer.
- Investigating bubbles – students work as scientists as they experiment with bubbles.
