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3.1.2        Towards a more sustainable water supply in cities

Considering that water around large cities is often polluted and cannot be used as potable water, a number of factors should be taken into account when seeking to reduce the vulnerability of large cities to water stress. These factors may include growing urban populations, improving lifestyles, reduced water availability due to climate change and the introduction of drinking water quality standards (EEA 2010).

The design of urban water supply infrastructure rests on a dominant engineering and supply-led approach in managing water dating back to the first stage of urban development and industrialisation. This is now considered outdated in an era of regional and global inter-dependence, technological development, economic restructuring and unprecedented flow of people, goods and resources (Kallis & Coccossis, 2001).

While centralized water systems have, in general, ensured adequate water supply, sanitation and drainage services in cities around the world (Sitzenfrei et al., 2013), several factors such as climate change, increasing water supply and consumption, as well as ageing water and wastewater infrastructures increasingly pose maintenance challenges to the cities.

To prevent urban water crises, water resources should be managed effectively at every stage: from the supply of clean water to its different uses by the consumers. This could involve reducing consumption (e.g. by means of technological improvements, water pricing schemes and non-pricing approaches to manage water demand) as well as finding new ways of collecting and using water (e.g. re-using rain and grey water) and reuse treated wastewater. Water management should also be better integrated within wider urban management while taking into account characteristics of the local environment (EEA, 2012c).

For instance, only a minor fraction of the high quality potable water provided by the centralized systems is currently used for potable purpose and most of the potable water is used for applications with low water quality requirements such as toilet flushing and garden irrigation. Under such conditions, the centralized water service model with the bulk transfer of freshwater and the bulk disposal of wastewater is not always the most sustainable solution for urban development (van Roon 2007). Decentralized water management is a concept in which water is managed, collected, treated and disposed/reused near or at the point of generation (Crites and Tchobanoglous 1998). Decentralized systems are increasingly considered to be implemented for two purposes; (1) to reduce flows to centralized wastewater treatment systems and (2) to provide opportunities for the wastewater reuse and recycling at the local level (Diaper et al., 2007).

One of the non-technological, non-pricing measures to manage water demand in large cities are awareness-raising campaigns. This approach has been used in Europe as a prevention measure as well as an emergency measure in the context of severe drought (e.g. during the severe drought that hit Barcelona in 2007-2008 (Martin-Orega and Markandya, 2009)). Given that this type of measures commonly aim at influencing household behaviour, their actual effectiveness is difficult to assess. Nonetheless, there have been interesting cases where the measures implemented could be directly associated to large scale shifts in water demand. Furthermore, when used in combination with other water demand measures, the overall effect can be stronger. For example, accompanying the promotion of water-saving technologies with educational campaigns that highlight their functionality and the appropriate way to use them can enhance the effect of the former (Cominola et al., 2015). The case of the project Zaragoza: Water Saving City is one that has resonated throughout Europe, evidencing the potential of a carefully structured awareness-raising campaign with clearly defined, concrete targets.