Rainwater harvesting and treated grey water systemsin buildings: Applicable European
Rita Ribeiro – Assistant Researcher at LNEC
Associated with population growth, climate change and the progressive of society the pressure on water resources has increased. Along with behavioral changes in water use and the use of more efficient devices, the use of alternative sources can reduce the pressure on water abstraction in the natural environment for the production of drinking water. Rainwater harvesting and the use of treated grey water for non-potable uses (e.g., watering green spaces and flushing toilets) are measures with high potential for reducing potable water consumption in urban areas. However, their application is not widespread in Portugal for various reasons. Standardization plays an important role in eliminating technical barriers and may be relevant in this case.
The European normative activity in the scope of wastewater engineering is developed by the Technical Committee CEN/TC 165 – Waste Water Engineering of the Comité Europeu de Normalização (CEN). The national monitoring of the normative activity of CEN/TC 165 is ensured by Technical Committee CT 90 – Water Urban System. European standards for the onsite use of treated wastewater are developed by WG 50 – Use of treated wastewater.
To date, two standards from a set of standards with the generic name “Onsite non-potable water systems” have been published: EN 16941-1 ” Sistemas de água não potável no local – Parte 1: Sistemas de aproveitamento de águas pluviais em edifícios “, published in 2018, and EN 16941-2 ” Sistemas de água não potável no local – Parte 2: Sistemas para a utilização de águas cinzentas tratadas “, published in 2021. Follows a presentation of these two standards, with reference to how their use could support the implementation of these water systems in Portugal.
The standards EN 16941-1:2018 and EN 16941-2:2021 aim to establish requirements for rainwater harvesting systems and treated grey water utilization systems, respectively. These standards provide recommendations for the design, sizing, installation, identification, commissioning, and maintenance of these systems. In EN 16941-2:2021, aspects related to water quality monitoring are also included, something that is not the case in EN 16941-1:2018. However, both standards refer to the f t-for-purpose approach, thus establishing that water treatment should aim to obtain characteristics suitable for the selected use(s).
The scope of EN 16941-1:2018 and EN 16941-2:2021 is restricted to non-potable uses, namely: landscape irrigation, toilet flushing, laundry, cleaning purposes (e.g. floor and vehicle washing). Both standards clearly identify the uses that are out of scope, namely: use for human consumption and food preparation; use for personal hygiene purposes; use for decentralized flow attenuation and rainwater infiltration (in the case of EN 16941-1:2018); direct use without treatment and consumption in heat recovery and cooling (in the case of EN 16941-2:2021).
Building systems defined by EN 16941-1:2018 and EN 16941-2:2021 consist of four main functional elements: collection, treatment, storage and distribution. According to these standards, it is important to consider the occurrence of excessive availability of water of local origin (rainwater and grey water) and, conversely, its scarcity. Thus, reference is made to the need to include properly sized overflow areas, to be activated when the maximum capacity of the system is reached. On the other hand, whenever the permanent availability of water at the points of use is required, these systems should include a complementary supply, usually with drinking water. This last aspect, the supply with backup water, is developed in the normative text with particular care, and minimum requirements are established for rainwater harvesting systems and treated grey water utilization systems in order to avoid contamination of the drinking water supply.
In both standards it is established the need to perform a risk assessment associated with the use of rainwater and treated grey water, considering the potential impacts on people, environment, infrastructure and equipment. This risk assessment should cover the design, installation, testing and commissioning, operation and maintenance phases of the non-drinking water system.
The clear identification of all components of rainwater harvesting systems and treated grey water utilization systems, including accessories and points of use of water, is another aspect that deserves special development in these standards. It is important to emphasize, for its relevance to the safety in the use of water, the requirement to place a sign warning of the existence of a non-potable water system near the supply valve of the building system of drinking water.
Despite the existing consensus on the recognition of the value associated with rainwater and treated grey water systems, several barriers have limited their widespread application in buildings.
Technical standardization can play an important role in removing existing technical barriers by standardizing procedures and criteria. The EN 16941-1:2018 and EN 16941-2:2021 standards are public domain documents that compile knowledge and methodologies validated at European level and establish guidelines for the design, sizing, installation, identification, commissioning and maintenance of rainwater harvesting systems and treated grey water utilization systems, respectively. Although their use is voluntary, it is believed that these normative documents can contribute to a greater use of rainwater harvesting systems and treated grey water utilization systems in Portugal, since they facilitate communication between the different agents involved and reflect the European experience in this field.
