By G.D. Zaney


Agriculture, more than any other sector of national economies, consumes the most of fresh water, with global estimates indicating that it is responsible for an average of 70 per cent of fresh water consumption.

Estimates from the Bonn Conference of 2011, indicate that the agricultural sector will have to produce 70 per cent more food in order to be able to cope with the expected increase in global population by a one-third, to 9 billion, by the year 2050, according to Malthusian projections.


One of the challenges for mankind and for existence on planet earth is sufficient food production which is closely linked to the availability of water — rain or irrigated —and the ability to manage it.


According to the International Water Management Institute (IWMI), cereal production, for example, will have to increase by 38 per cent to meet world food demands, which begs the question whether or not additional demand will provoke heavy investments in additional irrigation systems and whether or not increased area and yields from rain-fed agriculture can satisfy at least a substantial part of that demand.


Water is expected to be one of the most essential natural resources in the 21st century, with one-third of the world’s population experiencing water stress by the year 2025. In developing countries, particularly, water is said to be becoming scarce, water development increasingly expensive and, in some instances, detrimental to the environment.


What, then, are the options for ensuring a reliable water supply for agriculture?


A comprehensive assessment of water management in agriculture by Peter Droogers, David Seckler and Ian Makin and published in IWMI’s Working Paper 20, indicate that even though there is a large potential for rain-fed agriculture in many parts of the world, many other areas of the world require more irrigation to meet the food needs of their growing populations.


The assessment also comes to the conclusion that a large potential also exists for increasing food production through small-scale water-harvesting systems that provide partial irrigation.


In sum, it is suggested that patronage of salt water for irrigation will contribute significantly to food production, though at its current cost of production, desalinated water is considered not viable, economically, for most agricultural use—in view of the large amounts of water required for food production (1,300 and 3,400 litres of water for 1 kg of wheat and rice, respectively).


Statistics from the International Desalination Association indicates that currently, desalination plants use between 3.0 and 4.5 kilowatt hours of electricity, which means that the cost of desalinating water per cubic meter ranges between US $ 0.75 and US $ 1.25 for sea water.


Yet, there is evidence that desalinated water has become more affordable for high value crops such as fruit and citrus products which are less water-intensive (13 and 50 litres of water is required for one tomato and one orange, respectively).


Without doubt, desalination for agriculture is at its early stages of development and remains limited to high value crops, but improvements in technology and finding lower-cost solutions —through Public-Private Partnerships or interventions—can be considered to make it a more viable option in ensuring reliable water supply for food production.


The reuse of wastewater is another of the main options being considered as a new source of water in regions where water is scarce. In many parts of the world, untreated wastewater is employed directly for irrigation while water is also extracted from rivers which may be contaminated with wastewater discharged into the river with little or no prior treatment.


Available evidence suggests that the use of both types of wastewater have health implications such as the risk of gastro-intestinal diseases for farm workers and their families and for consumers of the farm produce.


In view of the health risks and considering the benefits of appropriately-treated wastewater irrigation to urban agriculture, guidelines have been drawn up to guide policy makers as to which wastewater treatment processes and irrigation methods are desirable for safe agricultural production.


The World Health Organization (WHO) 1989 guidelines and the United Stated Environmental Protection Agency/United States Agency for International Development (USEPA/USAID) Guidelines (1992), for example, have been said to be successful in creating awareness of the need for wastewater treatment and wastewater quality standards for agriculture.


It is to be noted, however, that many countries are yet to set wastewater standards while others are constrained by structural capacity or the financial resources to apply the appropriate wastewater treatment methods.


Notwithstanding the constraints, appropriate wastewater treatment is mandatory to   ensure that wastewater for irrigation is free of microbial contamination and to protect the health of farm produce emanating from wastewater irrigation.


Thus be it rain, desalination or appropriately-treated wastewater for irrigation, heavy investments are required in technology which, in turn, would require public-private partnership interventions.


The writer is an officer of the Information Services Department.

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