Barcelona Bets on Greywater: Sustainable Solution or Missed Opportunity?

Barcelona has taken a step forward in the fight against the water crisis with a new regulation promoting the use of greywater in buildings. But is it truly a transformative change, or does it fall short of the urgency of the moment?

A Regulation with Clear Objectives

At the end of June, Barcelona City Council approved the Greywater Reuse Ordinance, with the aim of advancing toward more efficient water management and fulfilling the commitments of the Pla Clima. This regulation establishes that newly constructed buildings — as well as those undergoing major renovations — must incorporate systems to recover and treat greywater.

The change is significant: it is estimated to affect 70% of new homes, 100% of hotels, and nearly 90% of sports facilities, with an expected saving of 136,000 m³ of drinking water per year. In addition, the measure is complemented by the expansion of the groundwater network, another alternative non-potable water source.

What Does This Mean for Citizens?

For those living in these new buildings, the regulation could result in lower drinking water consumption and, potentially, reduced utility bills. But beyond savings, it also aims to promote a culture of water conservation by involving citizens in urban sustainability.

Of course, things are not that simple. Installing these systems requires an initial investment that not all developers or property owners are willing — or able — to assume easily. Furthermore, keeping them in good condition involves ongoing technical and financial commitment.

Criticism and Missed Opportunities

Although the ordinance represents progress, it has not been free from criticism. Several social and environmental groups — such as CICrA Justicia Ambiental — have pointed out that the final text failed to incorporate many of the citizen proposals that emerged from the Sustainability Council. These proposals went beyond greywater recycling and included structural water-saving measures such as faucet aerators, dual-flush toilets, and mechanisms to monitor the consumption of major water users.

There has also been little commitment to establishing monitoring and enforcement mechanisms capable of guaranteeing real compliance with the regulation. The general feeling is that, although a step forward has been taken, an opportunity was missed to move toward a more ambitious and participatory model.

What About Biological Systems? A Technical Contradiction?

One technical aspect raising important concerns is the application of RD 487/2022, which regulates the prevention and control of legionellosis, especially considering the risks associated with the use of greywater. The municipal ordinance states that all treatment system components must be capable of withstanding disinfection procedures involving 30 mg/l of free residual chlorine.

This is where contradictions emerge: although the ordinance allows the use of biological systems — such as constructed wetlands or bioreactors with microorganisms — this type of disinfection is unfeasible for their operation. These chlorine concentrations seriously compromise the viability of many biological systems, and if the regulation requires periodic or preventive chlorination, such systems could become deactivated or destroyed.

Yes, the microorganisms could theoretically be “reseeded” after each chlorination process, but this implies additional costs, delays, and technical expertise that hardly fit the reality of a domestic or community-scale installation. The regulation appears to be designed more for physicochemical or mechanical systems, leaving unresolved how the real viability of biological alternatives will be guaranteed, despite being contemplated in the text.

Furthermore, there is no guarantee that biological systems can fully recover after shock chlorination, raising serious doubts about their long-term viability. As usual, responsibility ultimately falls on the installation owner, who must bear the consequences: proper design, maintenance, risk assessment, and potential costs arising from extreme treatment measures. The regulation allows natural solutions, yet at the same time places them in a very fragile position in relation to current health requirements.

The Road Toward a Resilient City

Despite its limitations, the new ordinance represents a paradigm shift. For the first time, efficient water use is being treated as a legal obligation in urban design. This could pave the way for more ambitious future measures, especially if other cities follow Barcelona’s example and refine the model.

However, for this transformation to become truly structural, it will be essential to resolve contradictions such as the one mentioned above and ensure that the regulation not only states which systems are permitted, but also creates the technical and legal conditions necessary for them to function effectively.

Ultimately, the question is not whether we should be reusing greywater, but why it has taken us so long to start doing so. In a context of climate emergency and water scarcity, every drop counts, and every decision — no matter how technical it may seem — reflects a model of city and society.