UNIT 4. THE HYDROSPHERE
WATER IS AN AMAZING SUBSTANCE.
Water: is a very common substance on the Earth and in other places of the Universe. On Earth, it is the only
substance that can be found in the three states in a natural way.
It is a chemical compound formed by molecules. Each molecule is formed by two atoms of hydrogen and one oxygen
atom (H2O).
The form and the nature of its molecules give water some astonishing properties:
- When the temperature goes down from 4 ºC to 0 ºC, water expands (the opposite of the other substances).
Therefore, when it freezes (at 0 ºC), the density diminishes.
- Frozen water, having a lower density, floats on liquid water. Thanks to this, in rivers, lakes and seas, fish can live in
winter although the surface is frozen.
PROPERTIES OF WATER.
• Water as a solvent: Water is the best known solvent. It dissolves almost everything, except fats.
• Salinity of water: Water can dissolve mineral salts, the quantity of mineral salts dissolved in water is called
salinity.
- Fresh water: It is called fresh water if it contains less than 1 % of dissolved salts.
- Salt water: It is called salt water if it contains more than 1 % of dissolved salts.
• Thermal properties of water: Water needs a lot of heat for its temperature to increase, but it also loses heat very
slowly (the other substances lose heat more quickly).
THE STATES OF WATER.
• Water in liquid state: Most of the water on the Earth is in liquid state.
There is liquid water in:
- Oceans and seas: They are formed by salt water and cover three fourths of the Earth’s surface.
- Continental water: It is generally formed by fresh water. We find it in: rivers, lakes, streams, torrents, lagoons,
ponds, wells, underground waters, etc.
- The clouds: they are formed by accumulations of very small drops of fresh water.
• Water in gaseous state: It is a minimum part and it is part of the atmosphere.
• Water in solid state: Most of the water in its solid state is concentrated in the Polar Regions. The rest is located in
very cold areas for example on mountain tops.
It is spread this way:
- The polar icefields: they are the ice layers that cover the Artic and Antarctic oceans (in the North and South
Poles).
- The glaciers: they are big masses of ice, accumulated on the Earth
THE WATER CYCLE.
• The water cycle: Solar energy and gravity put the water of the Earth in continuous movement.
It has three big stages:
1.- The water goes up into the atmosphere: Solar energy heats the water of oceans, seas, rivers, lakes, etc. The water
evaporates and goes up into the atmosphere.
The living beings also transmit water to the atmosphere with their transpiration.
2.- The water returns to the terrestrial surface: When it arrives to the high and cold layers of the troposphere, the
water vapor cools down and condenses. Clouds are formed and the wind makes them move.
Under certain conditions, the water falls down in the form of rain, snow or hail.
3.- The water circulates through the terrestrial crust: The terrestrial gravity makes the water move down. Torrents,
streams, rivers, etc. are formed, until they arrive to lakes, seas or oceans.
A part of this water infiltrates and forms the underground waters.
USES OF WATER.
• What do we use the water for?:
The consumption of water has increased alarmingly.
We use it:
- To satisfy the basic needs: feeding, hygiene, etc. (about 5 daily liters per person).
- To improve our quality of life: to wash, to clean, etc. (about 80 daily liters per person).
- To generate wealth: agriculture, industry, transport, etc. (about 3,200 daily liters per person).
- For recreational activities: maintenance of facilities, etc.
For most of these activities drinkable water is needed. Drinkable water forms a very small part of the terrestrial
water (2.5 %).
WE ARE DESTROYING THE HYDROSPHERE.
Water pollution: It is any alteration of the properties of water that can harm our health and the health of other
living beings. This pollution can be produced by waste waters, chemical substances, metals, plastics, batteries, etc...
• Exhaustion of the reserves: If we consume water faster than it regenerates.
• Changes in the environment: Big constructions like dams, reservoirs or highways can gravely modify the
landscape.
WATER MANAGEMENT.
• Quality water for all: We should watch over the quality of the water and commit to take care of it:
- In rivers, lakes, reservoirs, underground waters, etc. we should avoid putting in polluting substances and we
should not transform the natural riverbeds.
- Saving water mainly in agriculture, industries and in homes.
- To purify and to recycle water, we should purify the water of the cities before draining it into rivers or seas, or use
it for watering or cleaning the streets.
• Measures for sustainable water management:
1.- Rational extraction: That is to say to catch the water in times of abundance and to store it for times of shortage.
2.- Treatment and distribution: So that it arrives to all the points with quantity and in the appropriate condition.
3.- Reduce the consumption: By means of saving in agriculture, industry and in our homes.
4.- Purification of the waste waters: So that it can be reused or drained into nature without endangering people’s
health or the ecosystems.