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Heavy rainfall almost overflowing from a guttering system

Relieving water stress through rainwater harvesting

‘Accelerators’ are an exciting forum for solution-finding, inviting innovators to pit their wits against industry challenges. We sponsored and set five infrastructure-related problems for the TechFest Accelerator, run by New Civil Engineer magazine in October. Start-up StormHarvester won with its innovative solution to the pressing water scarcity dilemma many of our cities are facing.

How much rain falls on your roof? A business called StormHarvester reckons it can capture and reuse up to 95% of the water from attenuation tanks of average buildings. Therefore turning the attenuation tank into a valuable resource provider, with a low cost enhancement of the infrastructure already in place.

Even for building owners and occupants who enjoy well-tempered climates, the chance to cut utility bills should be attractive. But urbanisation and climate change make it more attractive still.

By 2050 the world’s population will reach 9.8B, estimates the United Nations (UN). Nearly 6.7B people are expected to live in urban areas. They are increasingly caught in the paradoxical situation of having too little water a lot of the time, while occasionally being flooded.

“Urbanisation combined with climate change are causing major problems,” says Brian Moloney, managing director of a start-up business called StormHarvester.

Today, 2.3B people live in water-scarce areas, says non-profit social enterprise World Data Lab. At our current rates of population growth and water consumption, half of all people will face water stress by 2030, predicts the UN. The water crisis that hit Cape Town, South Africa, between 2017 and 2018 serves as a stark warning of our dwindling supplies. Over 1B people globally are affected by flooding. As the effects of climate change worsen, scarcity and flooding are on the rise. In addition to flooding, more extreme rainfall events raise the risk that combined sewer systems will be overwhelmed and overflow.

StormHarvester proposes to solve the two problems in one.

“Imagine if we didn't have traffic lights controlling the flow of traffic in our cities,” says Moloney. “That's what our drainage infrastructure looks like at the moment. There is very little smart technology and smart control underground.”

StormHarvester’s solution brings precisely this smart element to drainage systems: almost every major new building is obliged to have an underground water attenuation tank. In the event of heavy rainfall, the tank fills, slowing the release of water into the sewer. Most of the time the tanks are empty – and StormHarvester sees this as a missed opportunity. By installing sensors and actively managing flow control, the tanks can be used not just to attenuate stormwater, but to store it. The key is to monitor weather forecasts and manage attenuation and storage pre-emptively.

“By linking the attenuation tanks to a weather forecast platform, we can predict when heavy rainfall is coming and empty the tanks in advance – so that when the stormwater begins to flow it can be held back. But, for all the smaller storm events, we can capture the rainwater,” Moloney says.

“We're able to capture and recycle about 95% of water that falls on the building. It gives us a source of water on-site that can be recycled for things like irrigation or toilet flushing. It essentially turns a stormwater management asset into a rainwater harvesting tank. And it’s available for every development, just by installing a small and relatively cheap piece of technology.”

Water efficiency plays a key role in addressing both climate change mitigation and adaptation. By recycling rainwater, residential and commercial buildings avoid drawing on the mains supply – meaning less demand for abstraction, treatment and distribution, with environmental, infrastructure and energy benefits.

“Once every few years, when we get a critical storm, the system is ready and prepared, because the forecast has instructed the tank to default back to flood prevention mode,” Moloney adds. “And that's where the key to the technology is: adding a digital element to what already exists, to make the infrastructure smarter and allow it to provide much more function than it does at the moment.”

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