Water water (isn’t) everywhere

Lisa Farnsworth of Stormsaver discusses how rainwater harvesting is critical to the design of future building design in the context of UK water scarcity

It is impossible to not notice the changes in weather conditions that we have been experiencing in the UK in recent years. June and July were scorching hot, and the water companies are all putting out advice on how to use less water. So, how can designers and specifiers ensure new buildings are water efficient and sustainable in an effort to manage our changing climate? The Environment Agency have predicted that we will soon no longer have enough available water in the UK to supply demand.

It makes perfect sense to collect rainwater locally from our roof areas and filter this on site, rather than wastefully sending it straight to drain to be transported and treated to drinking water quality, before being redistributed in the mains water supply. Over 50 per cent of our daily water use does not need to be treated to drinking water quality. For companies who wish to demonstrate a serious commitment to their sustainability agenda, rainwater harvesting is a must-have technology. Rainwater is hot news at the moment; too much of it, too little of it, how to manage it. How do you deal with and make the most of nature’s most abundant, free resource? Rainwater can bring life to those living in areas of water stress, but devastation in the form of flooding.

However, with expert management through rainwater harvesting and attenuation one of our most powerful resources can be harnessed, controlled and re-used, removing our water woes! We are living in an age where wastage is frowned upon and architects have the opportunity to lead the way in a sustainable water management approach, by utilizing rainwater harvesting in schools, offices, industrial and retail facilities across the UK. There are many applications in which harvested rainwater can be used. For example, WC and urinal flushing; irrigation and landscape watering; vehicle washing; laundry; and cooling or with fire sprinkler systems.

Rainwater harvesting can deliver significant returns on investment, especially with larger buildings with a high water demand, which may achieve a payback of between two to five years. Many buildings have roof areas, which conveniently can provide the right amount for their water demand. Rainwater is channelled from the roof into the storage tank passing an integrated vortex filter, which removes any large debris, leaves etc. Water enters the tank via an inlet calmer preventing disturbance to fine sediment on the base of the tank. Excess rainwater flows out of an overflow that has a one-way valve and rodent protection. Inside the tank are sensors and a submersible pump, which on demand take water from the cleanest part of the tank through a floating suction filter supplying filtered rainwater to the break tank in the roof space. This tank then gravity feeds water to point of use. For protection during periods of low rainfall a mains water top-up provides a continuous failsafe supply.

Attenuation tanks and crates can now also be utilised for storing harvested rainwater, hence the term “Active Attenuation”. Using intelligent weather predicting technology some systems can ensure that the available capacity of the tank is at a safe level should a storm hit the site. This means that the overall combined capacity of the attenuation and rainwater harvesting system can be reduced. Also, architects can add value to a client by converting their attenuation system into a rainwater harvesting system to save them money and water. Harvesting rainwater is now accessible, acceptable and critical to the way we design our future buildings. By acting responsibly and designing with consideration for future water shortage predictions we can ensure that our new building stock is as water friendly as it can possibly be.

Lisa Farnsworth is managing director at Stormsaver