What does it mean for citizens?
For residents of these new buildings, the regulation could translate into lower potable water consumption and potentially reduced bills. Beyond savings, it also aims to promote a culture of water conservation, engaging citizens in urban sustainability.
However, it’s not that simple. Installing these systems requires an initial investment that not all developers or owners are willing (or able) to make. Moreover, maintaining them properly demands ongoing technical and financial commitment.
Criticism and missed opportunities
While the ordinance marks progress, it has faced criticism. Various social and environmental groups — such as CICrA Environmental Justice — have pointed out that the final text did not include many citizen proposals from the Sustainability Council. These went beyond greywater recycling and included structural water-saving measures like aerators, dual-flush cisterns, or mechanisms to monitor high water users.
Furthermore, mechanisms for monitoring and enforcing real compliance with the regulation were not established. The general feeling is that although a step has been taken, the opportunity to move towards a more ambitious and participatory model was lost.
What about biological treatment systems? A technical inconsistency?
A key technical concern is the application of Royal Decree 487/2022, regulating the prevention and control of legionellosis, especially due to risks linked with greywater use. The municipal ordinance mandates that all treatment system components must withstand disinfection with 30 mg/l of free residual chlorine.
This is where contradictions arise: although the ordinance permits biological systems — such as constructed wetlands or bioreactors with microorganisms — this level of chlorination renders their operation unfeasible. Plants and bacteria that purify water cannot survive these chlorine concentrations, and if regulations require periodic or preventive chlorination, these systems would be deactivated or destroyed.
While it is possible to “reseed” microorganisms after each chlorination, this involves costs, delays, and technical knowledge that rarely fit the reality of domestic or community installations. The regulation seems designed for physicochemical or mechanical systems, leaving uncertainty about how the viability of biological options will be ensured, despite their inclusion in the text.
Moreover, there is no guarantee biological systems can fully recover after shock chlorination, raising serious doubts about their long-term viability. Ultimately, responsibility lies with the system owner, who must manage design, maintenance, risk assessment, and potential costs for extreme treatments. The regulation allows natural solutions but simultaneously places them in a fragile position against current health requirements.
The path to a resilient city
Despite its limitations, the new ordinance represents a paradigm shift. For the first time, efficient water use is legally mandated in urban design. This could pave the way for more ambitious measures, especially if other cities follow Barcelona’s example and refine the model.
For this transformation to be truly structural, contradictions like the aforementioned need resolution, ensuring the regulation not only permits certain systems but also creates the technical and legal conditions for their effective operation.
Ultimately, the question isn’t whether we should use greywater, but why it took so long to start doing so. In a context of climate emergency and water scarcity, every drop counts, and every decision — however technical it seems — reflects a vision for our cities and society.