Rainwater harvesting and use in urban buildings

The use of rainwater in buildings generally consists of collecting rainwater intercepted by all or part of the roof, storing it in a tank located in or near the building, from which it is redistributed to uses that do not require drinking water quality. This ancestral technique, which had disappeared from cities with the advent of centralized drinking water supply networks, has reappeared over the last 20 years – with a few adaptations – as an architectural practice for sustainable development. This return to the use of rainwater is a major trend that can be observed on every continent. In France, the trend began with the construction of experimental buildings, before specific technical regulations were introduced in 2008. It is now possible to use rainwater from inaccessible roofs for certain purposes that do not require drinking water quality. However, the correct installation of any rainwater utilization system –, whether simple (for seasonal watering) or complex (with water collected inside the building) – requires compliance with specific technical provisions set out in the decree and in various documents designed to support the players involved. Its design can also be considered as part of a broader approach to rainwater management on the scale of the plot associated with the building.

Based on the current state of the art, this article describes in detail these different aspects in a practical approach designed to meet the expectations of a wide audience, both professional (engineers, architects, planners, local authorities, etc.) and academic (teachers and students). It is divided into five parts. The first provides a general overview of the current development of this practice at international level and, more specifically, in France. The second part provides an analytical description of French regulations on the subject –, focusing in particular on the decree of August 21, 2008. The standard NF P 16-005 A comparison of French regulations with those in force in other countries is also carried out. French regulations are also compared with those in force in other countries. In the third section, the principles and various technical functions used to build the systems are described in detail. The fourth section outlines the technical requirements to be met, and the methods used to ensure that sizing is in line with the intended use. The final section describes the different configurations of rainwater harvesting systems that can contribute to urban runoff management.