Category 18 April 2019

Rainwater and greywater reuse systems in the Barcelona

Alternative water resources are gaining momentum in Catalonia (Spain) in an effort to promote water conservation and build resilience against droughts. Since 2002 more than 50 municipalities have approved a water saving ordinance that involves the installation of rainwater harvesting and/or greywater reuse systems in new buildings. Agenda 21 processes played a significant role in together with local governments.

The challenge

Increasing trends of urbanisation and growing number of urban population are expected to continue in the coming decades. This means that the demand for safe water supply will be growing as well. Furthermore, climate change will likely cause more frequent drought episodes, especially in semi-arid zones, such as southern Europe. Especially the Barcelona region has suffered from several droughts in the last decade.

The measure

In the metropolitan area of Barcelona, the Agenda 21 process has set the scene for a number of local regulations aimed at promoting sustainable practices of water. At the municipal level, water saving ordinances were put in place to mandate the installation of water saving devices such as water pressure regulators or dual flush toilets and enhancing the water and wastewater treatment, for instance through the (re)use of local water resources like rainwater, greywater and swimming pool water in new buildings. These new technologies trigger transformations in the existing water cycle including institutional and social changes related to water decentralisation.

The first municipality to approve the water saving ordinance was Sant Cugat del Vallès in 2002. In view of growing interest, the Diputació de Barcelona (provincial government) approved in 2005 a framework ordinance to help municipalities to develop their own ordinance. In 2006, national (Spanish) and regional (Catalan) authorities have been setting regulatory requirements and performance standards regarding the installation of water saving devices in toilets, showers and washbasins in new buildings. By the end of 2011, more than 50 municipalities in Catalonia - totalling over 1.3 million people - had approved the regulations for saving and conserving water.

Lessons learnt (Barriers, Success factors)

The introduction and enforcement of local regulations mandating greywater and rainwater reuse systems in new construction buildings appeared to be a major push factor for application and diffusion of these technologies in metropolitan Barcelona. Higher water prices can provide additional incentives for application of these technologies. While the current prices are still a weak incentive, water tariffs are expected to increase over time.

The social and technical lessons are an important component of implementing regulation on decentralised water reuse and recycling systems. The success of the implementation of the regulation and adoption of the technologies has been ensured by educating people on maintaining the technology as well as by promoting information sharing and public dialogue,

Many of the problems of the first installations have been taken into account and mitigated; more recent greywater systems no longer experience problems. Furthermore, maintenance costs have also decreased over the last decade.

Further deployment

The regulations and standards regarding water reuse in Barcelona are estimated to be 7 on the GML scale. The approach, which is incentivised by regulations and backed by strong participatory processes and voluntary agreements of citizens at the local level, strikes a sensible balance. Other arid regions can benefit from this example.



Domènech, L. & M Vallès. (2014). Local regulations on alternative water sources: greywater and rainwater use in the metropolitan region of Barcelona. Investigaciones Geographicas 61, pp. 87-96. 

Doranova, A. Implementation of greywater and rainwater reuse systems in the housing sector in the Barcelona Metropolitan Area. Case Study C.1. (p.101 ff) In ‘Screening of Regulatory Framework. Final Report’ Technopolis Group.