When I read about water scarcity and the issue of water wastage, to me it seems that it is inevitably related to the urban landscape. For instance, in today’s time, when the world is fighting the pandemic, organizations and governments are urging urban dwellers to use water carefully while washing their hands. The UNPD (United Nation Population Division), estimates that around two-thirds of the world population dwell in urban areas (UNPD, 2018). The demand for water in urban areas is increasing rapidly, and with an increase in the global population, the gap between supply and demand for water has widened. Also, depleting freshwater sources around the world is putting pressure on this valuable resource.
Globally, providing fresh water to the people and managing this scarce resource is a challenge for governments. This issue poses a greater threat in the developing countries as compared to the developed world. According to the UNPD, the global urban population is projected to grow by 2.5 billion urban dwellers between 2018 and 2050, with nearly 90 per cent of the increase concentrated in Asia and Africa. The water crisis in cape town served as an example of what lies ahead, following which a series of articles and research highlighted the cities that were faced with a similar threat. Agriculture is one of the biggest sector which uses a lot of water. On an average, agriculture accounts for 70 per cent of global freshwater withdrawal, and an increase in population is likely to put more pressure on freshwater resources (2017, FAO).
In this article, I discuss the usage of wastewater in agriculture and assess its impacts.
Use of Urban Waste Water in Agriculture
Both urbanization and agriculture demand huge quantities of water, and researchers are continuously working towards developing more sustainable ways of water use in both these sectors. There are a number of projects around the world that manage water resources in both these sectors, and one of the way to decrease the fresh water demand is by using urban wastewater for irrigation purpose in agriculture. Historically, the use of wastewater in agriculture is not something new and has been used by many civilizations like Mesopotamian, Indus valley, and Minoan (Angelakis et al., 2015). Presently, in some parts of developing countries, there are instances where farming practices in the peripheral areas of cities use wastewater generated through houses to meet their water requirement for agriculture. Regions in developing countries where water resources are scarce and farmers depend on precipitation and groundwater for irrigation, wastewater is often a reliable source for crop production throughout the year.
The use of urban wastewater not only help farmers grow their crops but also decreases the pressure on groundwater resources and reduces the outflow of wastewater into rivers, estuaries and wetlands. In this way, the high outflow of wastewater from urban areas does not pollute the freshwater sources situated in and around the city. Having access to large quantities of wastewater decreases the competition between farmers for water and allows them to irrigate their land throughout the year without depending on other sources of water. For instance, in arid and semi-arid regions where water is scarce and farmers are dependent on rainwater, groundwater and canals for irrigation, use of urban wastewater for irrigation not only provide farmers with a chance to grow crops throughout the season but also decreases their dependence on other sources of water.
The Cost of Using Urban Waste Water
The use of urban wastewater in agriculture is one of the solutions to the water crisis faced by several countries, especially those situated in arid and semi-arid regions of the world where frequent drought and water scarcity is the everyday reality. But this solution comes with a cost. Many developing countries which use wastewater in agriculture do not have sufficient resources and effluent treatment plants to clean the wastewater generated by cities, and often farmers use this untreated wastewater for irrigation. This untreated water is composed of organic and inorganic matter, nutrients, chemicals and pathogens. While several of the elements present in wastewater are useful for the growth of crops and work as a natural fertilizer, many of them, especially pathogens and chemicals, pose a serious threat to human health.
According to the WHO, several diarrhoea outbreaks have been associated with the consumption of vegetables irrigated with wastewater (2006, WHO). Consumption of crops, especially those eaten raw, may cause a serious threat to human health as they may be carriers of pathogens. In the case of chemical pollutants, the concentration of heavy metals in wastewater poses serious health hazards. For instance, one of the heavy metals, cadmium, is toxic to both humans and animals, affecting the kidneys and liver in a dose much lower than those that visibly affect plants (Jimenz et al., 2013). There are several other diseases and health-related issues occurring in people who are directly or indirectly associated with crops irrigated through untreated wastewater. Not only are people who consume the crop affected by pathogens and chemicals, farmers and crop handlers also face serious health threats.
The Way Forward
In this blog article, I have attempted to highlight the advantages and disadvantages of urban wastewater use in agriculture. As stated previously, increasing human population in urban regions will elevate the demand for food, and this demand will put pressure on the agriculture sector. In order to meet this demand, farmers will have to produce more, and therefore also consume more water, putting pressure on existing water resources. The idea of using urban wastewater in agriculture provides a solution to a big problem and may delay or in some cases even solve the water crisis. However, this solution comes with a cost to human health. While it is easy to present solutions such as treatment of wastewater and devise parallel quality control mechanisms for crops going into the market in order to prevent health hazards, most farmers using urban wastewater for irrigation belong to the developing or underdeveloped countries where the establishment of effluent treatment plants and their maintenance is not only difficult but sometimes not even a priority.
The solution to the problem is to provide a natural and cost-effective way of wastewater treatment, while also educating farmers to not use wastewater for those crops which are known to be consumed in the raw form. Crops can be categorized based on crop requirements, where non-palatable crops like cotton can be irrigated by untreated wastewater if treated water is not available. Finally, educational programmes for farmers not only provide solutions and save them from various diseases but also provide consumers with a healthy plate of food.
Angelakis, Andreas N.; Snyder, Shane A. 2015. “Wastewater Treatment and Reuse: Past, Present, and Future.” Water 7, no. 9: 4887-4895.
Jiménez, Blanca & Navarro, Ines. (2013). Wastewater Use in Agriculture: Public Health Considerations. Encyplopeadia on the Environmental Management, CRC Press Taylor & Francis Group, Editors: Jorgensen S., pp.2694-2708.
UNPD, 2018. World Urbanization Prospects: The 2018 Revision. United Nations Population Division, New York.
WHO (World Health Organization). Guidelines for the Safe Use of Wastewater, Excreta and Grey Water: Wastewater Use in Agriculture; World Health Organization: Geneva, 2006; Vol. 2.