The world is facing up to a potential water scarcity crisis, with two-thirds of the global population in danger of living in water-stressed countries by 2025. One of the biggest problems is the way we consume water.

Across the world, we use what is known as a linear water use model. This model sources water from groundwater and surface water supplies. Water is extracted from the source and then treated, distributed, consumed, disposed and collected, treated again and returned back into the water cycle for fresh extraction.

Water reuse: moving to a circular model

A more sustainable way of using and consuming water would be moving to a circular model and “closing the cycle”. This model would operate in a similar way to the linear model in terms of treatment, distribution, consumption, distribution/collection, and re-treatment. But instead of returning the water back into the water cycle for fresh extraction, it would be retained and reused.

This recycled water can be used for crop production or, if treated properly, like drinkable water supply.

The other key difference with a circular model is the potential for reusable water to be distributed in a more decentralized manner. This means that communities, organizations or even households can invest in water recycling systems to access a fresh supply of reused water.

Advantages of closing the cycle

The benefits of moving from a linear to a circular water use model include:

Lower environmental impact

The circular water use model is more sustainable than the linear model. This is because:

• it uses a recycled supply rather than extracting fresh groundwater supplies. Groundwater is a finite resource, with studies showing that less than 6% is replenished within 50 years. The extraction and pumping of both ground and surface water are also both energy-intensive processes requiring a lot of electricity.
• it reduces the pollution of water, which can become successively more polluted when released back into waterways via the linear model.
• If a decentralized distribution system is adopted, this also cuts down on environmental waste. Water has less distance to travel, piping networks require less maintenance and decentralized distribution systems are available that run on sustainable energy.

Availability of supply

Recycled water is more readily available than freshly sourced water. If systems can incorporate rainwater as well as treated wastewater, then this means access to a supply of water in no danger of running out. Although tap water through current centralized supplies is readily available in many countries, the dangers of future water shortages due to factors such as climate change and poor water management mean that this may not always be the case. In fact, global cities including Cape Town, Los Angeles, London, and Beijing are in real danger of experiencing a “day zero” where current supplies are restricted.

Cost-effectiveness

The circular water use model offers financial saving potential due to:

• lower extraction and treatment costs – water reuse eliminates expensive groundwater extraction costs which are generally passed onto the consumer. There is also the potential to lower treatment costs if rainwater is incorporated, as this contains fewer impurities than wastewater and so doesn't require the extra treatment technology.
• less infrastructure maintenance – the costs of maintaining the extensive and often ageing centralized infrastructure in linear water systems can be crippling and has been estimated as $41 trillion globally between 2005-2030. This includes maintaining large-scale sewage and treatment plants. The circular model permits a transition towards a cheaper decentralized management system.
• potential energy savings – treated wastewater has a higher temperature than freshly sourced water (around 10-20 degrees warmer). This means a reduction in water heating needs, so lower gas and electric costs!

Limitations of the circular model

Although a transition towards a circular water use model offers great potential, there are limitations that need to be factored in. Firstly, the technology for treating water for reuse, especially into drinking water, is not yet widely available. Systems such as the Q-Drop are now offering decentralized and sustainable reusable water on a small scale, it may be a while before this can be upscaled across large regions.

Secondly, it might not always be cost-effective for areas to transition to this model at present. Things need to be researched on a case-by-case basis, taking into account proximity to water sources, technological capacity, public perception and knowledge on water reuse, etc. 

Finally, there is a psychological barrier to water reuse. Not every consumer is ready for the idea of drinking treated wastewater, no matter how safe and cheap it may be. Much still needs to be done in terms of educating and persuading the public before we can make the leap to a fully sustainable water model.

Water Experts can help you with water sustainability and cost-efficiency. We aim to help build a more water-efficient future by providing a range of services including water audits, water reuse, and treatment technologies, research, and integrated sustainable water management.