In dry summers, there may not be enough water to irrigate agricultural and horticultural crops. Purified wastewater is a potential solution to this problem. This water may still contain some chemicals and pathogens (such as bacteria and viruses). These must not be harmful to humans, plants or animals. RIVM, Wageningen University and Research (WUR) and the Netherlands Food and Consumer Product Safety Authority (NVWA) have worked together to define a set of minimum quality requirements that this water must meet.
Chemicals
There are already standards for the presence of various chemicals in water. Limit values have now been established for the safe consumption of both vegetable and animal products, so that purified wastewater can be used for irrigation safely. These limit values have been compared with existing standards, with the most stringent one dictating the maximum permissible level for a chemical.
Pathogens for humans
A risk assessment has been carried out for bacteria and viruses that are harmful to humans. The amount of E. coli (the ‘poop bacterium’) is a key indicator of pathogenic micro-organisms that can be transmitted via faeces. The maximum permissible E.coli level in water depends on the vegetable type (i.e. to be consumed raw or cooked) and the irrigation method (i.e. leaf spray irrigation or otherwise).
Pathogens for plants
These pathogens are also common in the soil. The amount of additional pathogens in purified wastewater is negligibly small. The only risk is to greenhouse horticulture. This is because this often takes place in a sterile environment, where even small amounts of additional pathogens have the potential to cause harm.
Follow-up research in 2024
Further research will be conducted in 2024. This will involve a study of the risks of chemicals and pathogens to sources of drinking water. In addition, researchers will assess the risk to local residents and passers-by from the inhalation of water droplets released during spray irrigation.
Why this study?
Since 2020, EU (European Union) legislation has promoted the use of purified wastewater for irrigation in times of drought. The Netherlands implemented this legislation in 2023. The current study focused on the development of an assessment framework to ensure that humans, plants and animals are sufficiently well protected.
RIVM carried out this study in partnership with Wageningen Environmental Research (part of WUR) and the NVWA.