Eau Développement durable

Reuse of non-potable water: what are the health risks and possible solutions?

With water resources becoming increasingly scarce, there is growing interest in reusing wastewater and rainwater for irrigating crops, watering green spaces, washing floors and cars, or flushing toilets. However, this water may contain various pathogenic micro-organisms and potentially toxic organic or inorganic chemicals. Here are some explanations.

Why should non-potable water be reused?

Pressure on natural water resources is increasing due to urban, industrial and agricultural development and global warming. This pressure is increasing the scarcity of water resources and leading to a deterioration in their quality. It is therefore becoming more difficult to meet demand for enough good quality water for all the expected uses.

This has resulted in the growing reuse of different types of water to replace potable water. This reuse is one way of limiting the amount of water abstracted from natural resources.

In its water plan, the French government recently confirmed the benefits of reusing this water and set a target of developing 1000 projects by 2027.

Water reuse: a benefit/risk assessment

The reuse of non-potable water, wastewater in particular, involves storing and reusing water rather than discharging it into the natural environment. This therefore limits abstraction from natural resources.

However, in certain areas suffering from drought, these wastewater discharges would otherwise serve to replenish streams and rivers. Each project must therefore be analysed as a whole and the benefits/risks of reusing this water rather than releasing it into the natural environment must be weighed up.

In what ways can this water be reused?

Non-potable water can potentially be used for a wide range of purposes:

  • agricultural: for direct irrigation or supplying irrigation canals;
  • industrial: energy production, supplying cooling systems in air-cooling towers, car-wash facilities, making artificial snow, etc.;
  • urban: watering green spaces, washing roads, firefighting, district heating, etc.;
  • domestic: flushing toilets, washing clothes, cleaning floors and surfaces, watering vegetable gardens;
  • recreational: irrigating golf courses, supplying water to lakes, ornamental ponds (fountains, walls, etc.) or surface water bodies used for sports (swimming, canoeing, sailing, windsurfing, fishing), etc.
  • environmental: artificial recharge of groundwater, supplying ornamental ponds, irrigating forests or wetlands, etc.

In some countries suffering from high water stress, wastewater can be reused to produce drinking water.

However, because wastewater can contain various pathogenic micro-organisms and potentially toxic organic and inorganic chemicals, its reuse in France is regulated.


ANSES’s role

In the area of water reuse, the Agency conducts expert appraisals to assess the risks to health and the environment:

  • prior to establishing the regulatory framework;
  • in support of the competent authorities with draft regulations;
  • on experimental projects.

Its risk assessments take into account the hazards inherent in each type of water that is to be reused, the treatment methods available for the intended uses, and the control and monitoring measures required to manage them.


What water reuse solutions are currently authorised in France?

In France, the following uses of non-potable water are currently authorised:

  • treated wastewater from urban wastewater treatment plants can be reused for agricultural irrigation and watering green spaces;
  • industrial wastewater can be reused for washing roads, cleaning drains, supplying fire hydrants, etc.;
  • rainwater collected from inaccessible roofs (to limit contamination) can be used for washing clothes.

In addition, where health conditions are complied with, prefects may authorise the use of treated grey water for certain domestic purposes: flushing toilets, watering green areas, or washing outdoor surfaces without generating aerosols (i.e. without using high-pressure cleaners).

Reusing treated urban wastewater for watering green spaces or irrigating crops

In France, the reuse of treated urban wastewater is seen as a promising alternative for irrigating crops or watering green spaces. In certain situations, this practice could in fact help prevent water shortages and preserve water resources, mainly during periods of prolonged drought or in areas where water resources are scarce.

However, urban wastewater treated by sewage treatment plants contains various pathogenic micro-organisms and potentially toxic organic and inorganic chemicals. Since 2010, the conditions under which treated wastewater can be reused for irrigating crops or watering green spaces have been regulated, in order to prevent the health risks associated with this practice.

The work carried out by ANSES between 2008 and 2012 helped establish the French regulations governing the conditions under which treated wastewater can be reused for these purposes. In particular, ANSES stressed that professionals employed to carry out watering – as well as residents and bystanders – may be exposed to spray during such reuse of treated wastewater. As a result, the Agency issued a series of recommendations to supplement the regulatory provisions, in particular, specific technical requirements for spray irrigation with treated wastewater (maximum wind speed, safety distance) and recommendations for limiting the exposure of residents, bystanders and professionals by informing the public or prohibiting access to the site during and after irrigation.

Since 2020, the reuse of treated urban wastewater for agricultural irrigation has been governed by European Regulation (EU) 2020/741 of 25 May 2020, which sets minimum requirements for water quality at European Union level, depending on the use. French regulations needed to be brought into line with the provisions of this regulation, and ANSES therefore published an opinion on the draft order. 

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Reusing industrial wastewater for other purposes

Resulting from the AGEC Act against waste and for the circular economy, the Decree of 10 March 2020 authorises new uses for treated wastewater: road washing, cleaning drains and groundwater recharge. This broadening of possible uses should facilitate the emergence of new multi-use projects by making them more economically viable.

New projects for the reuse of treated wastewater will be authorised for a limited period. They will help advance knowledge and provide data on these new uses. The ultimate aim is to define national requirements in order to facilitate these practices and increase the volumes of treated wastewater reused in France.

Reusing grey water for domestic purposes

Grey water is non-potable water from showers, baths, washbasins, washing machines, and sometimes from kitchen sinks and dishwashers. Domestic reuse of treated grey water is attracting growing interest in France, but is also raising questions. This is because grey water is only authorised for certain uses, and by prefectoral dispensation on the basis of expert appraisals conducted by ANSES.

Based on the data available in 2015, the Agency believed that the reuse of grey water in homes could only be considered for strictly limited uses, in geographical environments that are prone to sustained and repeated water shortages. Subject to appropriate treatment and risk management measures, treated grey water may be suitable for three domestic uses, if it meets specific quality criteria:

  • flushing toilets;
  • watering green spaces (excluding vegetable gardens and agricultural uses);
  • washing outdoor surfaces without generating aerosols (i.e. without using high-pressure cleaners).

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Why are there risks in using non-potable water inside buildings?

The use of non-potable water in homes requires a separate network to be installed from the one supplying drinking water. Experience shows that the simultaneous use of potable and non-potable water in the same building can pose risks to people's health in the event of water mixing, misuse, loss of control, negligence or malicious acts.

Using rainwater for washing laundry

The practice of collecting rainwater and using it for domestic purposes has been on the rise over the past few years. This saves water and limits flooding through runoff.

However, as it passes through the atmosphere and runs off roofs or into storage tanks, rainwater can become laden with metals, organic matter, organic micropollutants and micro-organisms.

The Ministerial Order of 21 August 2008 lays down the conditions for using rainwater collected from inaccessible roofs, in buildings and outbuildings, as well as the conditions for installing, maintaining and monitoring the equipment needed for its collection and use. This order authorises the use of rainwater:

  • outside homes for domestic uses and watering green spaces;
  • inside homes for flushing toilets and washing floors.

At the request of the Directorate General for Health, the Agency conducted an expert appraisal in 2016 to assess the health risks associated with the use of rainwater for washing laundry in the home. Very few data on this practice are available. The Agency therefore recommended not using rainwater to wash the clothes of vulnerable people, mainly young children, immunocompromised individuals, people receiving hospital care at home, etc.

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