In an increasingly water-scarce world, there is no doubt that recycling water we’ve already used has to become normal. Part of that will inevitably mean using waste water to help grow the food we need. But will we ever feel comfortable using waste water for food production?
The reality is that this is already happening but more needs to be done to keep communities safe from the dangers of using untreated waste water.
The use of waste water for food production is mainly a question of managing water shortage and socioeconomic costs. Exponential population growth and climate change have seriously compromised water availability in many regions, from the Middle East to Africa, Southeast Asia and Latin America. Local communities urgently need to find solutions to the problem of increasing water scarcity.
If used properly, waste water can provide important nutrients for plant growth and act as a replacement for mineral fertilisers. But it should be used for agricultural purposes only after being treated. Unfortunately, in many regions of the world, the reality is far from that.
Agricultural and water policies have not sufficiently addressed the inherent threats posed by the use of untreated waste water for irrigation. Often, hazardous materials in the form of heavy metals, organic contaminants, pathogens or antibiotic-resistant bacteria can be found in waste water. These accumulate in soils, crops and groundwater and so pass into the food chain.
If evidence of the threats to human health and the environment are readily available, why are so many farmers still using untreated waste water for irrigation purposes?
In developing countries, the use of untreated waste water has one big advantage: it is cost-free. This means farmers use it for irrigation of crops without taking the necessary precautions to avoid public health risks.
Today, legally used waste water irrigates between 1.5% and 6.6% of farmland worldwide; about 10% of world’s food is produced using the practice. But the true extent of untreated waste water being used illegally for agriculture is unknown.
The Mezquital Valley in Mexico perfectly illustrates the issues involved. Rapid urbanisation and inadequate treatment facilities have led farmers in the valley to use untreated waste water from Mexico City for irrigation purposes. For more than a century, this practice has helped grow marketable crops at low production costs.
But these benefits come at the cost of the health of the population. The use of contaminated water for crops growth has resulted in severe gastrointestinal disease and cancer in the local community. Infants, young children, pregnant women, the elderly and people whose immune systems are compromised because of HIV/AIDS are especially vulnerable.
It is not a coincidence that the Mezquital Valley has the highest incidence of kidney cancer in the region as well as occurrence of helminth or Giardia infections in children.
Only by developing eco-friendly sanitation strategies has the reduction of water pollution loads while conserving the benefits of nutrients been possible. Since 1999, local waste-water plants have been built, and new wetlands have been constructed with satisfying results for water quality. But the people of the valley are understandably still sceptical about the benefits of treated waste water.
The experience of industrialised countries shows that even advanced waste-water treatment technologies struggle to address all risks. The presence of emerging pollutants and antibiotic-resistant bacteria in waste water are known to escape conventional waste-water treatment.
Needless to say, these contaminants are, even at low concentrations, a serious threat to human health. We need technologies and structured monitoring to ensure swift responses in order to keep communities safe.
There is no escaping the fact that our future food will be grown using waste water. Local communities like those in the Mezquital Valley can only do so much to protect themselves; regulations and government policies must be evaluated alongside the scientific evidence for the danger waste water can pose to human health. Only then can safe use of waste water in agriculture stimulate sustainable development in our water-scarce world.