Unblocking local systems

Decentralised water systems make sense in some settings, but cultural, professional and regulatory barriers have slowed their uptake. It’s time to change, writes Chris Davis.

Domestic and district water systems can be more affordable, water efficient and carbon smart.

Over the past 25 years a debate has emerged in Australia about the merits of dealing with water and sewage locally rather than in a few, central facilities for each city.

The localised approach has come to be known as ‘decentralised’, while the city-wide arrangement is called ‘centralised’ (there are more subtle definitions, but the general idea should be clear). Despite the long-winded conversation, no conclusion has really been reached yet; that’s not unexpected, given the conservative, risk-averse nature of the water business.

Circumstances have changed dramatically though, and we now need to acknowledge that decentralised water systems are legitimate contenders, under the right conditions. Firstly, capital is no longer as easy to come by as it used to be (even without the global financial crisis); and secondly, we need to make cities more sustainable, including their water systems. A system that is affordable, uses less water and has a smaller carbon footprint is more desirable than a costly, energy-hungry alternative that uses a lot of water.

The extremes on the spectrum are the fully centralised system with one water supply and one sewage treatment plant per city, and the fully decentralised model that features one on-site system per dwelling. Neither is that common – most communities tend to have hybrid systems somewhere between those poles, which is often the sensible response.

Adopting centralised water systems was a natural outcome of the drivers behind water and sanitation systems, starting in the late 19th century.

Water was piped in from a convenient source and delivered to homes and businesses in each community, mainly to support firefighting efforts but also to provide clean, safe water for personal use. Wells in towns tended to be contaminated, so river sources were preferable.

Once the connection between disease and faecal matter was identified, there was also a major push to pipe sewage out of the community and into the nearest river or on to a sewage ‘farm’ where animals or crops could be raised using the sewage.

From those beginnings, the typical 20th century water system arose, with the three separate water-related systems of water, sewage and stormwater, the latter designed to minimise the impacts of flooding on properties in the community. They operated in parallel, often by separate businesses, and any connections between them were problematic, like sewers overflowing into stormwater drains, or rainwater gaining access to sewers. To this day, water systems like that persist – they are the status quo.

Integration and irrigation
Despite the rump of water systems having the attributes listed above, ideas began to evolve based on the notion of integrating the three water systems. Firstly, some of the purified sewage could be put to use for purposes that didn’t demand drinking water quality, such as irrigation, cooling water for power stations, or process water for paper mills. Also, some of the rainwater running off roofs could be collected in tanks for home use – the well-known rural Australian rainwater tank, usually rolled from corrugated iron, has long been a feature of the landscape but fell out of favour in towns, only to be reintroduced in recent years thanks to persistent droughts.

In 1968, the desert town of Windhoek, in what is now Namibia, in southern Africa, took the drastic step of using its very well purified sewage effluent to supplement the town’s water supply when times were especially dry. Since then, several other cities, mainly in the US, have adopted a similar practice, now known as indirect potable reuse (IPR).

In light of the new ideas and in view of the fact that large water, sewage and stormwater networks are expensive to build and maintain, especially when tackled in large lumps – designed to cater for decades of future growth – the notion of building decentralised systems began to gain currency.

Internationally, decentralised systems have been strongly embraced in US practice and the concept of integrated urban water management has found many applications in Sweden, Germany and The Netherlands.

The concept sees a neighbourhood serviced by smaller sewers feeding a small sewage treatment plant to produce water for gardening and toilet flushing (two major components of domestic use) and relying on rainwater tanks to supplement the drinking water supply. Of the three urban water systems, water supply has been the least tractable to decentralisation, since collecting and using runoff (stormwater) in an urban context presents some major technical challenges.

Trial and transition
Moving from the traditional, centralised urban water system model to a decentralised one has encountered many barriers, some practical, some regulatory and some cultural. As a result, only a few dozen communities around Australia so far have embraced aspects of the decentralised model.

Because the configuration is still relatively new, it is often more expensive than the tried and tested centralised model, so the average developer is cautious about extra outlays. Because the interconnections and multiple sources and uses are complex, management can also be a challenge.

Australia’s world-leading approach to water quality management is now risk-based and validating the safety of a small system costs much the same as a large one, which militates against decentralised systems. Given our expertise in the area, however, it should not be beyond the wit of our practitioners to come up with cost-effective validation protocols that satisfy all stakeholders.

What has emerged recently is the concept of transition management, which recognises that achieving a major step change to a socio-technical system (like a water system) is not just a question of technology and cost, but a highly interconnected and complex question of cultural, regulatory and professional practices and perceptions. Expecting a technically feasible proposition for change to be accepted immediately is unrealistic – all the different facets of the system’s actors and gatekeepers have to be addressed together in light of the broader social and political context.

Pockets of change (niches) need to be enabled, free of regulatory barriers, so that policy and regulatory learnings can be extracted and applied in future. The water industry in Australia hasn’t adopted this approach yet, but there is a growing pool of people who understand this process, and their skills should be deployed.

The concept of integrating a water system is not incompatible with a centralised system, so every situation has to be examined on its merits – all can benefit from integration, but the precise mix of decentralised and centralised components will be unique to the local context.

Pragmatically, even if every new development across Australia were to be magically enabled to make as much use of decentralisation as was optimal, there would be a very slow transition from the status quo to a more sustainable future. For us to make a difference in less than 50 years or so, we also need to be retrofitting integrated and, where appropriate, decentralised water systems in our extant urban infrastructure, hoping to make a significant step towards sustainability in just a decade or two.

Chris Davis is Sustainability Business Development Manager at the University of Technology, Sydney and is also a National Water Commissioner.