The other day, I got some funny looks from a journalist who was interviewing me for an upcoming series on World Food Day. She asked me to list some of the ways I thought world hunger could be reduced. In addition to pointing to the need for better distribution of food and other resources, I gave my standard spiel about growing more food in cities. About half of the world’s population now lives in cities, which makes growing food there not just a hobby for wealthy urbanites, but an essential step in improving the health of the urban poor. But what made the journalist look askance was my description of how exactly urban farmers in some parts of the world are fertilizing their crops: with human manure and urine.
It may be hard for some of us to stomach, but much of the food grown in developing-world cities is irrigated with waste water. According to the International Water Management Institute, the reason is very simple—water from sewage systems is a low-cost, nutrient-rich source of irrigation for the urban poor. As a result, worldwide, 3.5 to 4.5 million hectares of land are irrigated with poop and pee. And while this sort of “waste” water can contain a whole range of pathogens, farmers can learn to use it safely. In fact, a Finnish study released earlier this week found that using human urine for irrigation can slightly increase plant growth (they used cabbages) and does not affect the nutritional value of the crop. In other words, urine can replace costly store-bought fertilizers and produce nutritious, organically grown food.
Although farmers have used human waste as fertilizer for centuries, cities and governments have more recently looked down on the practice. But in countries like Ghana, officials do not have the money or infrastructure to provide alternatives. In Accra, for example, 200,000 people a day eat salad from land irrigated with urine and human manure. But while this helps provide these folks a diversified diet, it also gives a sense of how many people may be at risk from polluted water. Educating farmers on how to grow, wash, and prepare urban food safely and educating policymakers about the agricultural and economic benefits of human waste will help ensure that millions of urban dwellers don’t go hungry.