Globally, eight in ten people are unsure of whether they will have enough water to drink, grow vegetables and breed livestock. Even when fresh water is available, it might not be clean enough for agricultural use and human consumption. And then the issue arises as to what ‘clean enough’ means.
Establishing what makes a water source good for agricultural use is the first step to sustainably managing this precious resource, which is under siege from climate change, land degradation, pollution and sprawling cities.
For 2019’s World Water Day, we asked International Water Management Institute (IWMI) senior researcher Everisto Mapedza what makes a water source good for agricultural use, such as for irrigation or the application of pesticides and fertilizers. Here’s what he had to say:
“It all depends on what you want to use the water for. You need a higher quality to irrigate vegetables that will be eaten raw, such as lettuces, than to irrigate pastures for livestock,” says Mapedza.
International guidelines tailor the physical, chemical and biological requirements of water to each use to ensure the safety of both producers and consumers of agricultural products. Poor quality can make people ill, affect crop productivity and damage the soil.
On the flip side, properly treated or diluted urban wastewater can help cope with the rising demand for safe water and food, as well as with growing volumes of waste, notes the IWMI senior researcher. “In the Middle East, for example, it is common to use wastewater for orchards and olive groves,” he says.
“What makes a good water also source depends to some extent on the social institutions, technology and infrastructure available for managing access, quality control and distribution,” state researchers from the University of Alaska.
The very same water source that could be unsuitable in one setting could be adequate in another, agrees Mapedza. “Well-resourced institutions than can monitor water quality are key to ensure it meets the minimum standards for its intended use,” he says. However, not all countries have compliance and enforcement mechanisms, or explore the linkages between water sources and public health problems.
Another determinant is infrastructure. In sub-Saharan Africa, for example, there is often a lack of means to harvest and transport water to its end users, meaning that 90 percent of its crops are rain-fed. And, the infrastructure must be of quality. “Even when dams are in place, we must figure out how to avoid them becoming breeding grounds for malaria-carrying mosquitoes,” says Mapedza.
The quality of water used for irrigation mostly depends on the type and quantity of the salts it contains, as they can accumulate in the root zone and reduce water availability to the crop. However, the kind and degree of problems salts can cause varies according to climate, crop and soil type, as well as the skills of the farmer, points out the Food and Agriculture Organization of the UN (FAO).
Ions such as sodium, chloride or boron can also accumulate in sensitive crops, damaging them and reducing yields. Other challenges mentioned by FAO are excessive nutrients, which can diminish crop yield or quality; unsightly deposits of iron or bicarbonate on fruits or leaves, which make products harder to sell; and abnormalities caused by an unusual pH.
Additional aspects to evaluate the quality of water are corrosion of equipment, which increases maintenance costs, and the proliferation of malaria- and other disease-carrying mosquitos when water fails to infiltrate the soil. Low-water infiltration rates – a problem in its own right – are influenced by salinity and the sodium content relative to the calcium and magnesium content.
International guidelines are essential, but farmers’ expertise can also contribute to sound decision-making. “For example, they look at indicators such as the presence of certain insects in the water to know if it is suitable for uses such as human consumption,” illustrates Mapedza.
“Listening to and engaging farmers can help us identify adequate sources in their territories and better manage them,” he concludes.
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