## Quantities of Water

We have an accurate idea of a litre of water, but do you know how much water there is in a cubic meter of air, or the quantity of liquid in a lake or an ocean? Do you know how much water is present when the Rhone floods the Camargue, or the flood required to create Valle Marineris on Mars? Do you know what quantity of water is ejected by a comet or is present in a cubic light year of interstellar matter?

And here is another task for you!

• Try and make an original contribution associating volumes of water on Earth and volumes of water in Space! Explain this to your friends and see their reactions.

### Surfaces

Water covers 70% of the Earth's surface, but 97% of it has too high a salt content (salinity) to be drunk by living beings or used in agriculture.

Fresh water thus only represents 3% of the total quantity of water. Some 70% of this is trapped in the polar ice-caps. Rivers, lakes and marshes only represent 1% of the total water on Earth. The remainder is underground water.

Sea water and ice represent 99.35% of all water on the planet Earth. The remainder is underground water, and that in streams, rivers, lakes, and the atmosphere.

Some 60% of rainwater evaporates and forms clouds; 25% penetrates the soil, and 15% flows into rivers and lakes.

The Earth's atmosphere contains 13,000 million tonnes of water. This is equal to a layer of water 2.5 cm deep, covering the entire surface of the Earth.

### Volumes

Now some numbers about the water on the Earth. First, here is how much water there is in the Earth's oceans:

OCEANS ON THE EARTH VOLUME OF WATER
Pacific Ocean 707.5 million km3 of water
Atlantic Ocean 323 million km3 of water
Indian Ocean 284 million km3 of water

The oceans cover 71% of the Earth's surface.

If the polar ice-caps in the Arctic and Antarctic melted completely, the average level of the oceans would rise by approximately 80 metres.

How much water flows in the rivers on Earth?. Here are some examples:

RIVER MIN FLOW MAX FLOW
Amazon 70 000 m3 per sec 200 000 m3 per sec
Congo 40 000 m3 per sec 80 000 m3 per sec
Yang Tsé-kiang 600 m3 per sec 50 000 m3 per sec
Danube 6 300 m3 per sec 22 000 m3 per sec
Rhine 780 m3 per sec 9 000 m3 per sec
Rhône 1760 m3 per sec 12 000 m3 per sec
Loire 75 m3 per sec 10 000 m3 per sec
Elbe 150 m3 per sec 3 600 m3 per sec
Seine 50 m3 per sec 1 650 m3 per sec

But the rivers also carry other things than water. As an example of the great pollution, here are a few numbers about one of the big rivers in Europe: Each year the river Rhone discharges between 2000 and 5000 tonnes of ammonia, 2000 and 13000 tonnes of chlorides, 300 to 700 tonnes of arsenic into the Mediterranean in addition to lesser quantities of copper, iron, titanium, cadmium,... Don't you think that this is a great pity?

And here we go again:

• Human beings are 75% water. Try to calculate what volume of water is contained in the 6 billion inhabitants on the planet Earth. Are you amazed?
• Try to calculate some other numbers and make other comparisons. You may send in your results to Sea & Space (address on the top page).

### Water Consumption

We use a lot of water for our daily needs. Here are the quantities of water required for domestic use (mean values for a European citizen; in some countries the quatities are less because of stricter regulations):

Activity Quantity of water used
Shower 25 - 100 litres
Bath 70 - 200 litres

Flushing the WC

8 - 12 litres
Washing dishes by hand 25 litres
Washing dishes by dishwasher 15 - 22 litres
Washing clothes by machine 55 - 120 litres
Washing a car 190 litres

Now try to answer these questions:

• If each person living on the planet Earth took one shower every day, how much water would be used in one year?
• Compare this with... (your choice!).