38
Another problematic aspect of large water distribution networks is that the
cross- connection of formerly separate water systems can lead to undesired ecological effects and the introduction of non-endemic species into an ecosystem. Manmade waterways (resulting in the interconnection of watersheds) have been
mentioned to be among the most important dispersal vectors of invasive aquatic
species (Leuven et al 2009 ).
3.2.3 Water Use
In general, societies and individuals use water resources in four major ways. We
distinguish between water for human consumption, water for food production purposes, water for industrial uses and water for the generation of (electrical) energy.
On a global scale, 70 % of the freshwater resources are used for agricultural
purposes, and only 19 % for industrial and 11 % for domestic purposes (including
drinking, washing, food preparation and sanitation) (FAO 2010 ).
Consequently, water needs to be treated according to the respective intended type
of usage. While the water for human consumption purposes requires elaborate treatment technologies, irrigation water in most cases remains untreated and is applied
directly to the arable land. Water for industrial processes is treated according to the
requirements of the intended usage.
A large proportion of the freshwater resources used by humans are fed into agricultural irrigation systems. These systems can be classifi ed according to their effi -
ciency. A simple defi nition of the term irrigation effi ciency refers to the ratio of the
irrigation water consumed by the crops of an irrigation farm or project to the water
diverted from a river or other natural water source into the irrigation canal (Jensen
2007 ). Effi ciency varies considerably among different technologies. For example,
subsurface micro- or trickle-irrigation in combination with mulch is among the
most effi cient schemes at present. Nevertheless, the actual effi ciency levels highly
depend upon the crop water consumption patterns, soil types, cultivation methods
and the automation grade (the most technically sophisticated systems use automatised soil moisture measurements in combination with computer-controlled water
and fertiliser applications and remote sensing systems).
Large scale irrigation schemes are in many cases installed for the cultivation of
so-called “cash crops” (crops for export), while crops for the local needs are in
many cases cultivated under rain-fed conditions (an example for this circumstance, the Fergana Valley in Central Asia, is dealt with in detail in Part III of this
volume). Cash crops contribute to the “virtual water” balance of nations and
regions by binding water in exported crops and thus to increasing the (negative)
water balance of the exporting country. “Virtual water trade” is a term used to
include the latent/hidden fl ows of water into water balances, e.g. if food or other
products are transferred from one place to another (e.g. Hoekstra and Mekonnen
2012 ). For example, the consumption of water for livestock farming and the export
of meat can be substantial.
S. Hoechstetter et al.
Another problematic aspect of large water distribution networks is that the
cross- connection of formerly separate water systems can lead to undesired ecological effects and the introduction of non-endemic species into an ecosystem. Manmade waterways (resulting in the interconnection of watersheds) have been
mentioned to be among the most important dispersal vectors of invasive aquatic
species (Leuven et al 2009 ).
3.2.3 Water Use
In general, societies and individuals use water resources in four major ways. We
distinguish between water for human consumption, water for food production purposes, water for industrial uses and water for the generation of (electrical) energy.
On a global scale, 70 % of the freshwater resources are used for agricultural
purposes, and only 19 % for industrial and 11 % for domestic purposes (including
drinking, washing, food preparation and sanitation) (FAO 2010 ).
Consequently, water needs to be treated according to the respective intended type
of usage. While the water for human consumption purposes requires elaborate treatment technologies, irrigation water in most cases remains untreated and is applied
directly to the arable land. Water for industrial processes is treated according to the
requirements of the intended usage.
A large proportion of the freshwater resources used by humans are fed into agricultural irrigation systems. These systems can be classifi ed according to their effi -
ciency. A simple defi nition of the term irrigation effi ciency refers to the ratio of the
irrigation water consumed by the crops of an irrigation farm or project to the water
diverted from a river or other natural water source into the irrigation canal (Jensen
2007 ). Effi ciency varies considerably among different technologies. For example,
subsurface micro- or trickle-irrigation in combination with mulch is among the
most effi cient schemes at present. Nevertheless, the actual effi ciency levels highly
depend upon the crop water consumption patterns, soil types, cultivation methods
and the automation grade (the most technically sophisticated systems use automatised soil moisture measurements in combination with computer-controlled water
and fertiliser applications and remote sensing systems).
Large scale irrigation schemes are in many cases installed for the cultivation of
so-called “cash crops” (crops for export), while crops for the local needs are in
many cases cultivated under rain-fed conditions (an example for this circumstance, the Fergana Valley in Central Asia, is dealt with in detail in Part III of this
volume). Cash crops contribute to the “virtual water” balance of nations and
regions by binding water in exported crops and thus to increasing the (negative)
water balance of the exporting country. “Virtual water trade” is a term used to
include the latent/hidden fl ows of water into water balances, e.g. if food or other
products are transferred from one place to another (e.g. Hoekstra and Mekonnen
2012 ). For example, the consumption of water for livestock farming and the export
of meat can be substantial.
S. Hoechstetter et al.