Case Study: 25 Rainwater Wall Panels Transform an Underground Car Park

When the operators of a large underground car park approached us, the brief was simple: find a way to harvest rainwater for site cleaning and landscape irrigation without sacrificing a single parking space or headroom clearance.

The Challenge

Underground car parks are notoriously short on spare floor area, and traditional cylindrical tanks or buried storage simply weren't an option. The site needed a solution that could sit flush against existing structural walls, survive a damp underground environment, and be installed without any groundworks or excavation.

The Solution

We specified 25 Rainwater Wall panels, wall-mounted along a long stretch of unused concrete wall throughout the car park. Each 225×175×30cm panel stores 1,000 litres, giving the site a combined capacity of 25,000 litres — all without touching a single parking bay.

The panels were connected in a modular run using standard globe valves and pipework, allowing the operator to isolate sections for maintenance without draining the entire system. The built-in leaf filter kept the harvested water clean even with run-off carrying dust and debris typical of a car park roof deck.

The Result

The completed installation now supplies water for pressure-washing the car park floor and for irrigation of the site's landscaped areas above ground — cutting mains water use significantly while turning a previously blank wall into a functional, tidy feature of the building.

This project is a good example of what makes the Rainwater Wall different from a conventional tank: it doesn't need a hidden corner or buried pit, it can go exactly where the space allows, including underground, wall-mounted, and in a fully commercial setting.

See more photos and video of this installation on our Projects page.