Why saving the rain adds up

SDS Intellistorm uses weather prediction data to control the levels of rainwater in a single tank so it can be used for both flood protection and reuse

Water recycling specialist Kevin Reed from SDS Limited explains how new technologies are making it increasingly commercially attractive for Scottish businesses to reuse water, just as the reasons for saving water are starting to add up.

SCOTLAND is a country blessed with plentiful supplies of water, but even such an abundant natural resource could be threatened as the impacts of climate change become evident.  Scotland has experienced periods of true drought conditions for the past couple of summers. Is it enough to make us think again about installing rainwater recycling systems?

Digital technologies are reducing the space needed for water recycling systems in new developments, and presenting better returns on investment for retrofitting, making them a more attractive prospect for bigger users. So much so, that SDS, a company known for its sustainable drainage products for controlling stormwater, saw an opportunity to acquire the water recycling business of one of the UK’s technology leaders, Waterscan, last year. It believes demand for water reuse products is set to increase, even in relatively plentiful regions like Scotland. 

The rainwater challenge

Meteorologists warn that global warming is extending periods of drought, while rainfall downpours become heavier and prolonged. These fluctuations, predicted to increase in future, present a joint challenge: How to be more resilient to the threat of flooding – and to ensure a continued, plentiful supply when water is scarce.

Flooding and drought are just two sides of the same water management coin. Yet, all too often we treat rainwater as a waste product, while at the same time throwing expensively and heavily treated drinking water – quite literally – down the drain.

According to Scottish Water, each person uses about 165 litres of drinking water every day – above the UK average. Does that matter if supplies are abundant? A least a third of mains water that has been extracted, treated to high quality drinking water standards and pumped to your door is used for non-drinking purposes.  

It could be as much as 60% for some commercial operations. Whether the water is used for flushing toilets in an office block, washing vehicles in a distribution centre or irrigating a market garden, heavily treated potable water is not needed.  

Yet, while in the disposal of other types of waste we accept the three-point priorities of “Reduce, Reuse and Recycle”, it is not a mantra you will hear very often applied to stormwater.

Water waste

It’s not just a question of water saving, there is a corresponding energy demand. Scottish Water is the largest consumer of electricity in Scotland. That means consuming water also has a carbon footprint. 

Reusing and recycling water on-site saves the carbon emissions associated not only with treating it and transporting mains water but also with treating it in the sewer network. Water use accounts for 6% of UK carbon emissions (about the same as the aviation industry). 

Apart from the benefits to Corporate Social Responsibility, the cold hard commercial facts may be starting to stack up for businesses. To begin with, there is the issue of security of water supply, which, even in Scotland, may no longer be guaranteed.  

The heatwave of Summer 2018 halted production at some Scottish distilleries, for example, and put severe pressure on many more which rely on natural supplies from local springs, rivers and burns. 

In May 2019, the Scottish Environmental Protection Agency issued water scarcity alerts throughout Scotland, river levels were very low in some places, and the more severely stressed Western Isles and Argyll regions were urged to take a range of measures to save water. 

Not much later, a wet summer had more than replenished the nation’s supplies. Any business who depended on water in the meantime, would have benefited from collecting the rainwater while it was plentiful.

 For heavy users of water, especially those with large areas of impermeable surface, be it hardstanding and car parks, or roofs, the justification for installing rainwater harvesting systems is strong. A supermarket can use water collected for staff and customer toilets; a rail depot uses rain water for train washing, a strawberry producer collects water from greenhouse roofs for irrigation. 

The SuDS hierarchy

Rainwater harvesting is not a new concept, but all too often the opportunities for reuse have been overlooked by designers of surface water drainage systems. Take a look at CIRIA 753, The SuDS Manual, widely acknowledged as the ‘bible’ for Sustainable Drainage Systems and referenced by consulting engineers and designers who design the majority of drainage schemes for developers. 

Not only does it identify rainwater harvesting as an important SuDS component, but clearly places reuse right at the top of the design hierarchy. 

One significant barrier to overcome has been the consideration of what happens if your rainwater collection tank is full and it’s still raining? To avoid flooding, and meet discharge consents, most designs require a second attenuation or storage tank.  Regulations require the collection tank to be able to store 18 days of water and an additional attenuation tank for drainage.  

This is can be costly, both in terms of capital and installation costs, as well as in land take.

SDS Intellistorm

So, would it not be better if the attenuation and rainwater storage tanks could be combined into one?  For a few years now, advances in ‘smart’ instrumentation, telemetry and cloud-based management and monitoring systems have been harnessed, by both academia and industry, in order to develop intelligent systems. 

SDS are now marketing the Intellistorm system, originally acquired from Waterscan, and are committed to further developing smart rainwater harvesting as a critical technology.

The central principle of SDS Intellistorm is the use of weather prediction data, downloaded via secure mobile phone signal, to control the levels of rainwater in a single tank for both attenuation and reuse. When a storm is predicted, the tank can be emptied in plenty of time to allow the spare capacity to be used as a defence against surface water flooding.

As a result, the costs of building and operating a rainwater harvesting system are significantly lower. What’s more, a digital cloud-based system, such as SDS’s SYMBioTIC, can also provide a wealth of data on system performance in order to better plan maintenance and demonstrate water savings in real time. 

 SDS recently provided a rainwater harvesting system to a large supermarket, which provides rainwater for a car wash facility and toilet flushing. The company has reduced its annual water bill by £4,500, making it able to pay back the cost of the RWH system in six years. Similar returns can be expected on distribution centres and leisure facilities, for example, and companies may be able to recover some of the costs of investment through the Enhanced Capital Allowance.

Every business case for rainwater harvesting is different, and expert organisations like SDS’ water recycling division, can advise on feasibility, correct sizing and work out the financial justifications for you. 

SDS is keen to talk to any commercial organisations who wish to partner with us in pioneering smart rainwater harvesting systems as a new sustainable technology that could be a true force for environmental progress in Scotland.