The Role of Rainwater Harvesting in Sustainable Water Management

Rainwater harvesting is defined as the collection and storage of rainwater before it is dispersed as surface run-off. Typically, a rainwater harvesting system collects the water running off a roof surface and passes it into a storage vessel.

It’s a process that is by its nature inherently efficient; simply put, rainwater is a water supply that is used where it is collected.

The water quality is typically high so it can be used for a wide variety of non-potable (non-drinking) purposes including WC flushing, laundry, garden irrigation and vehicle washing.   

Rainwater harvesting also has a recognised role to play in reducing flood risks. 

By storing the water from roof areas on-site and then passing the recycled water via appliances to the foul system rather than the storm drains, the system is able to lower peak flow rates.

In fact, in some countries (such as the UK) the installation of rainwater harvesting is now a necessity for gaining planning permission where an area could be at risk of flooding or where the mains water simply cannot support demand and requires back-up.

And harvesting rainwater can also help satisfy an increasing consumer demand for “green” and “sustainable” homes.

Business and property owners are becoming increasingly aware of both the environmental and economic benefits of improving water and energy efficiency.

For example, in the UK with its temperate climate systems, it’s estimated that reusing rainwater can lower mains water use in commercial applications by up to 80 percent and in domestic homes by around 55 percent. In other countries (for example, Australia) this percentage can be even higher - up to 100 percent depending on the climate, how the tank is used, water efficiency and the tank size.

Not surprisingly, the financial savings for building owners who have water meters can be significant.

Rainwater harvesting also means that homeowners are less affected by water restrictions during periods in which community water supplies are under strain. 

There are other, perhaps less obvious, economic, and environmental benefits to installing rainwater harvesting systems.  For example, they can reduce the need to build new dams, or desalination plants, and cut water infrastructure operating costs.

Rain and stormwater harvesting can also lessen the environmental impact of urbanisation on stormwater drainage systems and receiving water bodies.

Surface water run-off from heavy rainfall collects pollutants such as fertilisers and trace metals. If this then flows into natural waterways, it will change their composition and ecological make up.  And polluted waterways ultimately flow into our oceans.

Excessive runoff can also cause flooding, putting additional pressure on city infrastructure in urban areas - including municipal/highway drainage systems that were never designed to cope with the loadings placed upon them.

Installing large numbers of rainwater tanks in urban areas increases the retention potential of the catchment and reduces the frequency, volume and peaks of storm water run-off.  This eases the strain on stormwater infrastructure and reduces the impact on the environment, which would otherwise bear the brunt of a stormwater surge.

There are other more tangible benefits to capturing and reusing rainwater, for example, to support urban “green” spaces.  Protecting and promoting green spaces (such as domestic and rooftop gardens and parks) is vital for any healthy urban environment because they can limit the impact of rising temperatures and climate change.

Urban micro-climates tend to be significantly warmer than vegetated areas because their widespread hard surfaces absorb, store and radiate heat. By contrast, vegetation provides shade and cools the air through a process called “evapotranspiration.”  However, maintaining urban green spaces can be water intensive so rainwater harvesting can provide a sustainable source of water to irrigate these valuable green spaces.

Rainwater harvesting should be regarded as an essential component of global integrated water management frameworks and is expected to be a major international policy issue in the 21st century.

We are already seeing countries adopting new planning policies, water efficiency standards and rebates, all of which should encourage the proliferation of rainwater tank use in countries across the world.

There is a clear need for architects, designers and builders to consider incorporating rainwater harvesting into new projects as traditional, centralised water supplies become less viable. The growth in apartment living, for instance, creates exciting opportunities to incorporate rainwater tanks and other sustainability features into rooftop spaces.

In this market landscape, building industry professionals need to have the skills and knowledge to create smart, sustainable homes and urban spaces to stay competitive.