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INTRODUCTION• Since the Dublin conference in 1992 it is

widely accepted that water is a scarce resourcethat should be treated as an economic good.

• The term ‘virtual water’ was introduced byTony Allan in the early 1990s (Allan, 1993;1994).

• The water consumed in the production processof an agricultural or industrial product hasbeen called the 'virtual water' contained in theproduct (Allan, 1998).

continue…• If one country exports a water intensive product to

another country, it exports water in virtual form.

• For water-scarce countries it could be attractive to

achieve water security by importing water-intensive

products instead of producing all water demanding

products domestically (WWC, 1998).

• In this way some countries support other countries in

their water needs. Reversibly, water-rich countries

could profit from their abundance of water resources

by producing water-intensive products for export.

WHY THE WATER TRADE IN VIRTUAL FORM

• Trade of real water between water-rich and water-poorregions is generally impossible due to the largedistances and associated costs, but trade in water-intensive products (virtual water trade) is realistic(Hoekstra and Hung, 2002).

• Virtual water trade between nations and evencontinents could thus ideally be used as an instrumentto improve global water use efficiency, to achievewater security in water-poor regions of the world andto alleviate the constraints on environment by usingbest suited production sites (Turton, 2000).

• Primary product (Cereals, vegetables and fruits)

• Processed products (sugarcane, oil)

• Transformed products

• By-products (cotton seed oil)

• Multiple-products (coconut, animal)

• Low or non water consumptive product (sea food)

Water efficiency

• In most studies on virtual water for food, the basic value ofvirtual water only considers the water evapotranspired atfield level.

• However for irrigated agriculture, water losses either for thefield application or during the distribution must be consideredif there is no possibility of recycling these losses at basin level.

• It might be useful to introduce a correction coefficient toinclude them as proposed by Haddadin (2002).

• Furthermore water leaching sometimes required in arid areasto deal with saline water must also be considered as waterconsumption.

Production efficiency

• For multi annual food products the period and thelevel of production varies with time.

• The estimation of the virtual water value must takeaccount total production and water consumptionduring life span.

• For instance for perennial vegetal products, or fordairy production, the effective period of productionis reduced as compared to life span, and this must beconsidered as a reduced production efficiencycompared to peak yields.

Consumption efficiency

• Production at the farm gate does not entirely convertinto consumption because of various wastes beforereaching domestic consumption, and also theprocess itself of food consumption generates its ownwaste.

• This is particularly true for fresh products (vegetables

fruits) which are sensitive for conservation.

Steps in the calculation of global virtual water trade

Ref. crop evapotranspiration E0 [mm day-1]

Crop evapotranspiration Ec[mm day-1]

Crop water requirement CWR [m3 ha-1]

Specific water demand SWD [m3 ton-1]

Global virtual water trade VWT [m3 yr-1]

Virtual water content for some crops

CROP WATER REQUIRED (mm/crop period)

CROP YIELD (t/ha) VIRTUAL WATER CONTENT(cubic m/t)

Sugarcane 1101 69.0703 159

Paddy 852 2.9892 2850

Wheat 438 2.6482 1654

Sorghum 320 0.7895 4053

Millet 264 0.8075 3269

Related terms

• Since the beginning of the 2000s, when the concept of“water footprints” was additionally introduced.

• The water footprint of a nation is defined as the totalvolume of freshwater that is used to produce the goodsand services consumed by the people of the nationwhich usually includes water resources consumed inother countries in the case of import goods („exogenouswater“).

• This linkage of the problems of water scarcity,agricultural trade and food security is oftentimesdenoted as the „water‐food nexus“ (Allan 1998, p.545).

CONCLUSION

We are theoretically understanding the concept“virtual water trade”.The world nations are interdependent by themeans of their demands and resource availability.The knowledge eyes are only zooming the thingswhich are produce huge impact over our life cycleand so Allan introduced the term virtual watertrade.