This Technical Report is applicable to the installation of rainwater infiltration and storage/attenuation systems under gravity. This Technical Report covers installations including: reservoirs made by assembled cuboid shaped thermoplastic boxes; integral components; ancillary components (e.g. access provisions and connections); geotextiles and/or geomembranes; embedment and backfill. These systems are intended for underground use in landscape, pedestrian or vehicular traffic areas and are used outside building structures. This Technical Report is only applicable to systems containing boxes to create a reservoir where the manufacturer has clearly stated in the installation instructions how the components should be assembled. This Technical Report is a guidance document. It provides a set of general guidelines which gives best practice for installation. NOTE 1 It is anticipated that additional recommendations and/or requirements (e.g. design, dimensioning and structural aspects) will be detailed in the relevant standards.