Земельные и водные ресурсы

Reused water as a resource

Javier Mateo Sagasta, FAO specialist on Water Quality and Environmental Aspects of Irrigation, talks about the global use of water resources and solutions to avoid wastage. He says: "Water reuse is a crucial factor to implement a sustainable management of the water cycle." 

3rd of May 2011. FAO Headquarter, Rome.

Is there a global water crisis? If so, is this linked to food? 

I prefer to say that water is primarily a local and regional issue. However, in many regions of the world the demand exceeds the available supply of water resources and this leads to water scarcity, a problem that will worsen in the future. Water is a key resource for food production. Globally, agriculture uses more than 70% of total water withdrawals, but in some developing countries agriculture use is as high as 95%. The global food production therefore needs to make better use of water resources and avoid wastage: produce more food per liter of water is key. Water reuse and recycling is part of the solution and a crucial factor to implement a sustainable management of the water cycle. Irrigated agriculture must be modernized and for that investments are needed. Developed countries have the financial resources and can afford it, if there is political will, but developing countries may face important financial barriers to access this technology and to go through a modernization process.

How can we overcome this gap between rich and poor? Is it possible to bring the model of sustainable water management to developing countries? 

It is possible and should be done, also in developed countries where it´s still a pending task. In poorer countries we also have to secure an economically, environmentally and socially sustainable development. Water technologies that have been successful in rich countries are not necessarily valid for developing countries. Normally the costs of these technologies make them not-applicable in the low-income countries. This is the case of wastewater treatment technologies for reuse in agriculture. There have been cases where export of western patterns and technology to poor countries resulted in a total failure: high-tech sewage treatment plants are installed with funding from rich countries, but beneficiaries have neither the training nor the financial capacity to operate and maintain them. The result is money poorly invested and no purified sewage. However, there are low cost technologies, easy to maintain and tailored to the socioeconomic conditions of developing countries.

Is reuse of wastewater the last option for those who lack other? 

Is it a reliable water source?

Water demand is growing globally and conventional water resources are limited. The use of non-conventional water resources for irrigation, such as treated wastewater, is an option that is becoming increasingly important in arid areas. This offers many opportunities for all, for example the farmers that obtain water and nutrient resources throughout the year, for instance nitrogen, essential for plants, is abundant in the urine. Cities and the environment can also benefit. Cities can get conventional water from agriculture in exchange of treated wastewater. Consequently urban users will be provided with more high-quality resources at a reduced cost, compared to alternative supplies. Agriculture can act as an alternative tertiary wastewater treatment by up-taking nutrients that, if otherwise discharged to water bodies, may cause environmental problems such as eutrophycation and hypoxia.

It should however be said that the wastewater has pathogens and chemical agents and their use in agriculture can pose serious health risks. To minimize these risks, a proper wastewater treatment is an essential option to consider. Furthermore, treatment should also be accompanied by the selection of proper irrigation and cultivation practices. For example, when using drip irrigation to water fruit trees, the treated waste water is not in direct contact with the fruits, minimizing the risk for any pathogens to spread to the consumer.

Are there any standards or guidelines specified for the use of sewage in agriculture? 

Several countries, including many European ones, have laws and regulations for the reuse of water specifying the water quality needed for different uses. To achieve these stringent water quality standards, the required treatments are often very expensive. In many developing countries these requirements are perceived as unattainable and therefore ignored. FAO, WHO and UNDP have developed international guidelines, offering a flexible methodology for the safe use of wastewater, excreta and greywater. We believe the key is to combine different options to protect consumers and farmers health. For example, you can get vegetables without pathogens by combining basic debugging with the use of drip irrigation and washing the final product.

In some countries, water is harvested. Is this possible? 

Yes, it is possible and practiced. Rain water harvesting refers to the collection of surface runoff for productive use. Instead of letting the water flow and cause erosion, it´s harvested and used. This practice is not new in arid and semiarid climates, but an old tradition in many cultures. For example, rainwater is collected on the roofs of houses and stored for domestic or irrigation purposes in many places around the globe. This is an increasingly common alternative for watering gardens and urban agriculture.

FAO says when water is scarce, there is no single solution to ensure food safety. What does this mean? 

Water is essential for any economic development, to combat hunger and maintain healthy ecosystems. Water scarcity is an imbalance between the availability and demand. To combat water scarcity, the available water can be increased, regulated or better management. But we may also reduce water demand by reducing wastage's in the food system. For example, it is estimated that 50% of food produced is lost or wasted on its way "from the field to the fork" and this means a lot of wasted water. Keep in mind that to produce one kilo of wheat 2,500 liters of water are approximately needed and to produce a kilo of meat about 25,000 liters of water are required. These figures makes it clear that if the food consumption pattern of developed countries is adopted worldwide, with excessive consumption of meat, water shortages will be aggravated.

Agriculture as a user of marginal water >>