Water Cycle Management: A New Paradigm of Water Reuse for Cities of the Future

Water shortage is a dire concern in many countries and regions of the world as a result of population growth and urbanisation. In a context of scarcity, water reclamation and reuse are becoming increasingly prominent as alternatives to meet different water consumption needs. Although there is no longer any question on whether or not used water should be reused; there are definitely many questions on how to reclaim and how to use the water efficiently and safely.

Although it is possible, technologically, to remove all the pollutants from used water to make it suitable for any purpose of reuse, conventional urban water and wastewater systems have not been designed in a way that reclaimed water can be easily introduced into the existing system as a “normal” water source.

The facilities for reclaimed water production, distribution, and supply are, in most cases, like “abnormal” patches on the existing system; and the efficiency of reclaimed water utilisation is also very low. Even for newly developed cities and towns, the design of the water and wastewater systems usually still follow the conventional approach.

In recent years, scientists and engineers have begun to reconsider our water and wastewater systems, which originated from the systems born more than a century ago, when the world’s population was less than one-seventh of the current population and natural resources, including water, were regarded as plentiful. It is clear that for efficient water use and the maximitation of reclaimable water sources, we need to not merely apply short-term technological fixes, but redefine and innovate in the design of urban water and wastewater systems. .

To reclaim and reuse water is virtually to create a new water cycle. Therefore, water cycle management becomes a topic of public concern for managing water reclamation and its uses in an efficient and safe way. Water cycle management isn’t new terminology in the hydrological field. Yet, the introduction of the concept into urban water systems, especially water reuse, only began recently in many countries; and then only to meet the needs of a growing population under conditions of insufficient water resources.

If we recall the history of human utilisation of water resources, we can say that water utilisation has gradually evolved from natural dependence to engineering dependence.  Early human settlements took water directly from nature, only later building aqueducts to supply water to small-scale cities. Used water discharge or disposal was also done in completely natural ways through direct discharge into natural waters.

These extremely simple methods for water and sanitation did not result in any noticeable contamination because the scale of water utilisation was very small; and not sufficient to compromise the capacity of self-purification of natural waters. The turning point to what we call modern urban water systems was in the 18th century as a result of the industrial revolution, which brought about the birth of modern cities in Europe and then America and other continents. Provision of pipe networks covering the whole service area is the first feature of the modern urban water supply system.

In a time when natural water was still thought of as plentiful, the modern urban water and wastewater system was characterised by water use and discharge in the “end-of-the-pipe” manner; namely using large quantity of water not only for portable purposes, but also for “washing out” wastes and discharging the used water to a water body as far from the urban area as possible.

The modern urban water and wastewater system is itself an engineered pathway for water to flow, including several stages of water quality conversion such as drinking water purification and wastewater treatment. One of the important reasons for this shift is the rapid increase of ecological footprint due to a growing population and economic development. It is estimated that in 1970 the global ecological footprint began to exceed the global biocapacity, and in 2010 the former was already 1.5 times of the latter, indicating that we need one and a half planet Earths to accommodate human beings.

Under such conditions, it is emergent for us to consider how to save the limited natural biocapacity. A promising way to start is to rethink the conventional design of urban water and wastewater systems, because they’re no longer suitable to respond adequately to the current situation of limited available resources and biocapacity.

Accelerating innovation on the topic of water cycle management for sustainable urban development is at the core of the IWA World Water Congress in Brisbane, from 9 to 13 October, 2016

Xiaochang Wang is interviewed by Corinne Tommsdroff, manager of IWA’s Cities of the Future program. Xiaochang Wang tell us the story of the programme (2:00), but also about urban metabolism (2:46) and how science learns from natural ecosystems (5:56). The interview ends with the new paradigm for cities (7:00), where resources are limited and recycling is imperative.

Xiaochang Wang

Xi'an University of Architecture and Technology, China; IWA Journal Editor