‘New regulatory and legal framework for water reuse calls for an interdisciplinary approach’

Connection lies at the basis of responsible application of safe water reuse.

In 2020 the European Union approved a legislative proposal on the requirements for water reuse in irrigation applications. Commissioned by the Ministry of Infrastructure and Water Management, KWR investigated the implications of the proposed guidelines for the situation in the Netherlands. In the resulting published report, the researchers conclude that an interdisciplinary approach is called for. This will make it possible to weigh up the benefits and the risks of wastewater reuse. KWR researcher Milou Dingemans: ‘Each case raises specific questions.’

The availability of freshwater is under pressure. The reuse of water can alleviate the problem, but the approach taken must be tailored to the specific circumstances. A shift therefore needs to be made from the ‘safe discharge of wastewater’ to the ‘responsible reuse of wastewater and its purification for the targeted use.’ Such a shift demands not only a change in mindset, it must also be reflected in legislation. However, legislation on the responsible reuse of water in the Netherlands and Europe is today still in its infancy.

Various guidelines

It is true that there are already various published guidelines which have been developed all over the world, like those of the World Health Organization (Guidelines for the safe use of wastewater, excreta and greywater in agriculture and aquaculture, 2006; Guidelines for potable reuse, 2017). In Israel, water has long been extensively reused. In Australia and the US, as well, water reuse has for quite some time been seen as a valuable solution to growing water stress, and appropriate regulations have been formulated for its use. The Australian National Health and Medical Research Council (NHMRC) has established the Australian Guidelines for Water Recycling for agriculture (2006) and for augmentation of drinking water supplies (2008). And in the US, the USEPA Guidelines for Water Reuse of the Environmental Protection Agency (EPA) (2012) have been implemented, and Title 22 is in force in the state of California (CPDH 2015). But how far have we come in Europe with such laws and regulations?


EU legislative proposal for water reuse for irrigation

Work has been ongoing for several years in the EU on legislation on responsible water reuse. The proposal to this end that was approved by the European Council in 2020, following its successful passage through the European Parliament the previous year, is titled: ‘EU regulation on minimum requirements for water reuse for irrigation’. Together with a number of her colleagues, KWR toxicologist Milou Dingemans already examined the document at an earlier stage. ‘The EU wants to use the proposed guidelines to support and stimulate the responsible and safe reuse of wastewater for irrigation’, says Dingemans. ‘This is being done through the harmonisation of minimum quality requirements, risk management, licensing and the sharing of relevant information.’

Other forms of water reuse

Although this represents the first steps in European legislation towards deploying WWTPs as alternative irrigation sources for agriculture and horticulture, it still does not concern other forms of water reuse. The European Parliament has however indicated that the assessment of the legislation should also examine whether the rules are also applicable to other forms of wastewater reuse, such as in groundwater recharge and the irrigation of parks, sports pitches and golf courses. The European Parliament also wants to incorporate an exception clause into the legislation to allow for innovative pilot projects. Following publication as European legislation, work is now underway on implementation in the Member States.

Minimum quality requirements

Dingemans: ‘In 2018 the Ministry of Infrastructure and Water Management asked KWR to investigate the implications of the proposed guidelines for the situation in the Netherlands, to provide guidance for voting in the European Parliament. The resulting research report has been made public and is accessible for everyone to read. In our evaluation we examined, among other elements, the minimum microbial and chemical requirements, the proposed Water Reuse Management Plan, as well as the impact that the guidelines would have, based in part on practical case studies.’

Comments on the microbial requirements

The KWR microbiologists commented on the minimum microbial quality requirements in the 2018 guidelines. Thus, E. coli (the ‘poop bacterium’) was chosen as the indicator organism to make it possible to determine, on the basis of its numbers, the presence or absence of pathogens in the water. However, we know that E. coli is much more easily inactivated in water treatment processes than are viruses and protozoa. A misleading picture of the health risks might therefore result if only these bacteria are taken into consideration. This objection is only partly addressed, in the case of crops that are eaten raw – so that possible pathogens from the irrigation water are not neutralised through cooking – by mandating monitoring for the presence of more persistent organisms, such as bacteriophages (viruses that can attack bacteria) and bacteria in spore form.

The researchers also concluded that it did not really make sense to set minimum requirements for the presence of Legionella species in general. It would be better to focus on Legionella pneumophila, which causes Legionnaires’ disease, or legionellosis. This is particularly relevant in the application of reused water in sprinkling, since legionellosis is spread primarily through spray. In addition, it would seem important also to include noroviruses and adenoviruses and the eggs of parasitic worms in the minimum requirements. ‘Our observations about the microbial requirements mean that the regulations should take more account of the diversity in the properties of pathogens, whereby the context defines whether these differences are important,’ says Patrick Smeets, who is an expert in microbial safety of water reuse at KWR. ‘The challenge is to derive a clear regulatory approach from this complexity.’

Chemical requirements not elaborated

With respect to chemicals in reused wastewater, Dingemans notes that the legislative proposal does not elaborate any associated minimum requirements. ‘The existing regulations in the area are referred to. The implementation is thus subject to interpretation, while one still cannot exclude the possibility that irrigation with reused wastewater could lead to exposure to undesirable substances, such as metals or emerging unknown compounds. This is why it is important to closely examine what innovations are needed for responsible water reuse.’

Water Reuse Management Plan

To determine the potential risks associated with the reuse of wastewater, the EU legislative proposal requires the supplier of the water, in every case, to draw up a Water Reuse Management Plan. ‘This encompasses the key elements of a risk-management plan,’ explains Dingemans. ‘It describes what you want to do, where the water will come from, what you will use it for exactly, and how it will get to the site where it will be used. What are the hazards involved in each of these steps for humans, animals, the environment and occupational safety? Do these risks call for additional requirements, beyond the minimum quality requirements outlined above?

‘A good Water Reuse Management Plan should present a viable and practical approach to identifying and managing risks. In practice, however, it is difficult for a water supplier to get the right information needed to properly underpin such a plan, in part because the supplier frequently does not have a view or control over the entire chain (from supply to irrigation application). This is why it is extremely important that all stakeholders and responsible parties work together to ensure that this can be effectively brought about.’
Milou Dingemans PhD
Milou Dingemans PhD

The different steps in the development of a Water Reuse Risk Management Plan, as established in the current EU legislative proposal for water reuse in irrigation.

Interdisciplinary risk management

Dingemans has a firm conviction when it comes to the risk management. ‘You can’t do it on your own; it is an interdisciplinary activity. You need knowledge from several sectors. Not only the supplier of the water, but all involved actors and stakeholders, including the public authorities, must contribute their specific knowledge and information for the picture to be complete. If you assign all of the responsibility to the water supplier – usually the Water Authority that runs the WWTP – then the latter will first have to do a great deal of work before a permit can be requested and the water reuse begin. And getting the required information is not a simple matter. Moreover, according to the new EU regulation, the water supplier must then invest a great deal of time and money in the mandatory monitoring. But in meeting this obligation, the supplier runs up against the limits of its sphere of influence. It’s all a pretty complicated business. Under these circumstances, I can well imagine that a potential supplier won’t be too readily inclined to respond to a request by a horticulturalist or farmer who is interested in using treated wastewater for irrigation. The EU regulation could, in the worst case, discourage stakeholders who wish to directly try out the use of treated wastewater.’

But this does not mean that water reuse does not yet take place in the Netherlands. Researchers from Utrecht University, KWR and Deltares have indeed recently shown that, particularly in periods of drought, great use is already being made of surface water containing relatively high concentrations of discharged treated wastewater. This indirect reuse arises on its own whenever a WWTP discharges treated wastewater into surface water, from which water is then later drawn for irrigation. And this ‘unconscious’ reuse is not subject to any EU requirements or safety measures at all.

Opportunities for improvement

Dingemans: ‘It would be incredibly unfortunate if the regulations were to unnecessarily stand in the way of direct water reuse. In many instances, effective regulation and monitoring leads to better risk management, and contributes to the necessary increased awareness and acceptance of reuse.’ Among the means of improving the legislative proposal, the researchers are thinking of broader guidelines and directives, for example for preventive measures and for actions in emergencies. Building in buffer systems can, for instance, help prevent situations in which the supplied water has already been used for irrigation, while the monitoring results show that it does not meet the quality requirements. Additionally, when the risks of direct water reuse are being assessed, it is important that the right reference situation be chosen. In the Netherlands this is the use of groundwater or surface water, and the latter already involves the effluent from WWTPs. Unregulated, unintentional and indirect wastewater reuse also entails possible risks and inefficiency factors, which today remain uncontrolled and unknown.

Enthusiasm, but still a long road ahead

Dingemans notes that the ‘EU regulation on minimum requirements for water reuse for irrigation’ elicited immediate interest in Dutch political circles. ‘I saw a couple of tweets along the lines of: “Great, that’s what we’re going to do!” Such enthusiasm makes me very happy. But, at the same time, I also ask myself: Where can those horticulturalists go who are so keen to start irrigating with reused water? Do they knock on the door of their Water Authority? And how does the Water Authority respond, in the current situation in which there is still no Dutch law? And how should it respond, soon, when we do have such a law? Where will it then get the information it needs to assess whether direct reuse, in a specific case, is responsible, feasible and sensible? In short: there is a vast array of questions and uncertainties that need to be clarified.’

Start right now with an interdisciplinary approach

Dingemans and other (KWR) colleagues have not limited themselves to asking these questions; they also recommend an interdisciplinary approach in which the benefits and risks of wastewater reuse can be weighed against each other. ‘This is necessary for the design and realisation of wastewater reuse that is safe and responsible,’ says Dingemans. ‘This requires the collection of information about water demand and supply, water quality and health, technology and the regulation of various kinds of applications. Each case raises specific questions. Does demand for freshwater actually decrease if you replace it with treated reused wastewater; and, if so, by how much? What are the relevant health risks presented by pathogens or chemical compounds in the reused wastewater? And which treatment methods do you therefore give preference to? Which laws and regulations need to be complied with? And who are the responsible public authorities, and which stakeholders are there in each part of the reuse process? And are they sufficiently involved in the process? More than enough complexity, it seems to me, to demonstrate the need for a broad, interdisciplinary approach.’

Publication as a starting point

The above-mentioned publication written by the researchers about this interdisciplinary approach is intended as a starting point and invitation for a collaboration between all relevant sectors and scientific fields. Dingemans: ‘We have to quickly find a way of building a good regulatory and legal framework together with all of the stakeholders. There already exists a whole set of knowledge systems, data bases and practical measures, which can help implement direct water reuse responsibly. KWR is able and willing to play a role in this: with lots of relevant disciplines in-house, we dispose of a broad knowledge base that can contribute to the development and realisation of knowledge, cases and practical applications. We are moreover used to connecting partners from various sectors and scientific fields, with a view to addressing difficult water issues. For example, we organise webinars for this purpose. I look forward to the moment when we will have built up a solid body of knowledge, from which all stakeholders can draw so as to actually get busy with the responsible reuse of water: the sooner, the better.’