(*) related to the HUMAN USAGE chapter of FYR Checklist
Worldwide, the largest use of water is for agricultural purposes (70%), followed by industrial activities, (22%), and the smallest amount is used for domestic use purposes (8%).
The situation varies among continents, both in relation to consumption (e.g. per capita water consumption is much lower in Africa than in Europe), and in relation to sectors (e.g. in Europe and North America the use in industrial sectors prevails, while in all the other continents water is mostly used in agriculture).
(*) related to the HUMAN USAGE subchapter 1 - Agriculture
Irrigation dates back to early times, and was already practised by the Babylonians, Egyptians, Incas and Romans. In ancient times, agriculture flourished in great river alluvial plains, where plenty of water was available. In the Nile delta, the periodic floods brought water and silt to the ground, and increased the fertility of the soil.
The method of irrigation is based on distribution of water by flowing and infiltration in the soil by force of gravity. Water from a river is diverted and distributed through a network of channels (questions 1 a-b-c).
Agriculture has not only developed in areas of the world where regular precipitations make the soil very fertile and moist, but also in dry regions where agriculture completely relies on irrigation from water intakes such as rivers, lakes and underground aquifers (questions d-e). The consumption of water for irrigation depends on the kind of cultivation: for example, about 500.000 litres of water are required to produce 1 ton of wheat, but even more than 4 millions litres are required to produce 1 ton of rice.
In agriculture a lot of water is often wasted because of obsolete canals, pipes and other inefficiencies, but sustainable irrigation methods exist such as using brackish water and purified urban sewage. The method of drip irrigation is also more efficient than the classic method of canal irrigation: water is distributed only where it is necessary. This method helps to reduce consumption by 60%, and improves production because crops receive water only at proper times and in appropriate amounts.
Intensive agriculture requires lots of water, it often degrades water quality and can also decrease the quantity. In fact, deeper and deeper wells are dug to find water in dry areas and during drought periods.
Furthermore, the risk of contamination on surface and underground water by agriculture is extremely high (questions f). Polluting agents are mainly fertilizers and pesticides, which are spread on farmlands to increase production and control unwanted insects, plants and other animals (questions h-I). Nitrogen, phosphorus and other compounds often found in these products and disperse from farmlands into surface and underground waters when not absorbed, producing such conditions as the afore mentioned eutrophication caused by a high concentration of nutrients (question g). Natural barriers, like riparian vegetation zones and wetlands on the edges of the fields and along the riverbanks are often removed to increase production and help mechanic means, but should in fact be restored and preserved because they are able to stop nitrogenous and phosphorated chemicals from reaching water bodies.