Water is an essential factor of production in agriculture. The Men very quickly depended on agriculture. A lack of water (dryness) caused famines as well as a water overflow (floods).

The ground has a role of tank. Indeed, a plant pushes constantly whereas the rain or the irrigation is specific. The ground absorbs water then yields it to the plant. The ground contains water most of the time, but in different concentrations. The Canadian ground is much wetter than the ground of the desert thus the plants which push there are not the same ones. The plants of the desert save water whereas the trees of the large forests of the northern hemisphere rejects a great part of it.

Water is an important factor for the growth of the plant for it is necessary to photosynthesis. Photosynthesis is the chemical reaction which makes it possible the plant to grow, i.e. to manufacture its carbonaceous matter. It indeed needs water, rock salt and sun.

Today, modern agriculture provides for all the needs for the plants while irrigating regularly and by providing the matter mineral in the form of artificial fertilisers or natural. This knowledge makes it possible to the farmers to cultivate out-ground. The plants live in solutions which contain only what they have need to live.

The Man invented several systems to irrigate his cultures. He diverted rivers, builds structures. But these transformations sometimes caused ecological catastrophes like l’èchement of the sea of Araal. The rivers in the countries of the Middle East are prone to many covetousnesses and to create tensions between the countries. Water remains a major capital for its countries. The countries which have the river upstream pump its water which misses then with the country which has the river downstream. The wars of the future could be started because of these problems...