Setting health based targets for water reuse (in agriculture)

WHO published in 1989 the first Guidelines for the Safe Use of Wastewater and Excreta in Agriculture and Aquaculture that were widely used. Since that time, more experience has been gained and more evidence is produced. The new WHO guidelines on water reuse in agriculture, recently published, provide all the basic information on the health risks, and how to set health based targets, by quantifying the risk and developing pathogen reduction targets. Furthermore, an analysis of the health protection measures is included, making reference to the wastewater treatment, crop restrictions, wastewater application methods and human exposure control.

The new guidelines on the safe use of wastewater arrive in a critical period of time, when the climate change effects have already started to occur in a number of European countries, mostly Mediterranean, in the form of sudden floods and/ or by absence of rainfall. The methodology described provides all the necessary background and furthermore the mechanism to adopt a treatment scheme for sewage, so that if used for irrigation, the health risks are minimized. But in addition, it bridges in the most accurate way the legal framework followed in the US (California), which was very severe, with the WHO guidelines issued in 1989, that contained less stringent measures. The proposed methodology has the advantage of being quite flexible and not rigid and proposes to the countries a number of alternatives to select from. In fact, it is not acceptable to ask developing countries to adopt strict criteria and standards requiring high degrees of treatment and consequently excessive funds for investments and running expenses for their economies. Sewage treatment for further use in irrigation, should follow methods that are compatible with the local climate conditions and affordable by the countries. Therefore, countries are free to choose from the suggested alternative methods, those that fit their climatic conditions, are affordable, and by combining them with a series of barriers, they can achieve the health based standards set for the quality of the treated water to be used for irrigation.