The expansion of urban areas is unmistakable to anyone who finds themselves within a city. A simple glance at the number of tower cranes highlights the ongoing transformation of our skylines. Even with just three years of experience in the construction industry, I have witnessed firsthand how spatial constraints present significant challenges in these environments. From increasingly strained public transportation systems to the urban heat island effect, these issues underscore the urgent need for innovative solutions to meet the ever-growing demands of our cities.

Flooding and drainage are among the most pressing concerns, with the construction industry placing a considerable burden on existing infrastructure. Local water authorities are under pressure to upgrade their assets to cope with rising demand, driven by an increase in impermeable surfaces, higher volumes of foul water discharge, and reduced natural areas for water absorption.

As a result, site-specific surface water discharge restrictions are now mandatory for all major developments, including refurbishments that connect to existing, often near-capacity, private drainage networks. With limits on the volume of rainwater allowed to leave a site, developments must now retain and release water at rates that mimic those of greenfield (undeveloped) land. This has made attenuation storage volume a critical factor in project planning.

Over the past year, the introduction of Schedule 3 and the UK Government’s National Standards for Sustainable Drainage Systems (SuDS) has formalised a runoff destination hierarchy. This guidance places a strong emphasis on rainwater harvesting, which is now a preferred and—in some cases—an essential requirement by Lead Local Flood Authorities (LLFAs). The runoff hierarchy is as follows:

Traditionally, rainwater harvesting may be associated with passive systems—such as directing runoff into soft landscaping or collecting it in simple rainwater butts. However, more advanced systems enable active reuse within buildings for non-potable applications like toilet flushing or irrigation. These systems not only reduce water bills but also improve water efficiency, support sustainability goals, and protect the environment. They can reduce mains water consumption by up to 30% and lower a building’s carbon footprint. Additionally, because these systems are typically located in plant rooms, they are more accessible and easier to maintain than buried attenuation systems.

To push innovation further, smart tank systems offer a dual solution: managing both attenuation and rainwater harvesting. These systems recognise that attenuation tanks are often empty, especially during dry periods, and use this capacity for rainwater storage. By integrating weather forecasting data from the Met Office, smart tanks can automatically release water in advance of storms, ensuring sufficient capacity for attenuation. There are already a wide variety of manufacturers encapsulating these techniques like Stormsaver’s active attenuation and greywater recycling systems exemplify this approach.

At Whitby Wood, we are currently implementing smart tanks in three projects, including one in Westminster, London. This site involves a two-storey extension, and the LLFA has required a minimum 50% reduction in discharge rates. Given that the building footprint occupies the entire site and the extension will use TLC construction, traditional attenuation options like blue or green roofs are not viable due to loading constraints. This makes it an ideal case for smart tanks. By placing the tank on top of the basement slab, we ensure easy access for maintenance and future replacement, unlike buried SuDS systems, which are often difficult to access.

As urban areas continue to expand at an unprecedented pace, the pressure on existing infrastructure, particularly drainage systems, has become a critical concern. The shift toward sustainable development demands not only compliance with evolving regulations, such as the UK’s national SuDS standards, but also a proactive embrace of innovative technologies. Rainwater harvesting, once seen as a passive measure, is now a vital component of modern drainage strategies, especially when integrated with smart systems that optimise both water reuse and attenuation.

By adopting intelligent solutions like smart tanks, developers can address multiple challenges simultaneously: reducing surface water discharge, enhancing water efficiency, and ensuring long-term resilience of infrastructure. These systems exemplify how engineering can evolve to meet the complex demands of urban living, balancing environmental responsibility with practical design. As demonstrated in our projects, such approaches are not only feasible but essential for shaping sustainable, future-ready cities.