Addressing water scarcity requires reduction of use and improved water-use efficiency. This includes water reuse, shifts to less demanding crops and industries, water rationing, improved agricultural practices, and use of virtual water trade accounting for embedded water costs. However, even higher water-use efficiency sometimes does not meet community needs, requiring development of additional water sources (e.g. rainwater harvesting, desalinization, fog interception). Water is transferred across large distances and even between drainage basins in arid regions (e.g. Salem 2009). Management strategies and technological improvements outlined here address water scarcity and stress.
Water efficiency
Improved water efficiency is central to the water-food-energy nexus, considering factors such as climate change, population and land use (Fader et al. 2016). Water efficiency refers to reducing water wastage, in contrast to water conservation, which focuses on reducing water use. To this end, growing food demands require increased productivity per litre of water. Increased water efficiency could also result in reduced water use for energy production, assuming a gradual transition to non-fossil fuel energy sources. Rapid urbanization requires protection of water sources, reduction of reticulation losses and increased water in storage.
Efficiency gains across sectors and regions have been realized through technology and management improvements. As the largest global water user, agriculture represents the greatest potential in water-use efficiency. However, inadequate global data exist to accurately evaluate the overall state and trends of industrial and domestic water-use efficiency. The UN-Water Integrated Monitoring Initiative, initiated in 2014, attempts to address the water-related global monitoring gaps (UN-Water 2017). Existing data are informing the transition from the MDGs to the SDGs, but spatial distribution and frequency of measurements need to improve to strengthen water-resource monitoring, modelling and management.
Desalinization
Desalinization addresses water scarcity in arid regions and large coastal cities such as the Gaza Strip on the Mediterranean Sea (United Nations Office for the Coordination of Humanitarian Affairs [OCHA] 2017). About 60 per cent of global desalinization occurs in arid West Asian countries (e.g. Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, United Arab Emirates) (Abuzeid 2014; Abuzeid et al. 2014; UNEP 2016c). It is also becoming more common in California, United States of America and eastern Australia, which are prone to recurrent drought years (Little 2015; UNEP 2016a).
Impacts of desalinization include large energy demands, associated greenhouse gas emission risks, the effects of heavy brine releases into coastal ecosystems (Jenkins et al. 2012), and entrainment of marine organisms in infrastructure (Dawoud and Al Mulla 2012). The desalinization industry is working to mitigate these impacts and advances in membrane efficiency and energy efficiency may reduce the cost of doing so by 20 per cent over the next five years, and up to 60 per cent over the next 20 years (Voutchkov 2016).
Water rationing
In water scarcity conditions, water authorities and governments must prioritize water allocations to specific sectors and users. While rationing mechanisms are usually determined by legal water rights, there may also be emergency measures protecting the public and the economy (see also Box 9.4).
Water reuse
Water reuse or reclamation is the concept of treating wastewater as a resource, rather than as variably contaminated waste discharged to the environment (UNESCO and WWAP 2015). Reclaimed water is most commonly used in developed countries for non-potable purposes (e.g. agriculture, landscape and park irrigation), thermal power plant cooling, industrial processes, and enhancing natural or artificial lakes and wetlands (UNEP 2016a; UNEP 2016c). Singapore uses recycled water for indirect potable use and for direct non-potable use. Windhoek (Namibia) uses it to recharge aquifers which thereafter feed water into the bulk water supply. Recycling treated wastewater provides multiple benefits by decreasing water diversions from sensitive ecosystems and reducing wastewater discharges to surface waters, in addition to being a dependable, locally controlled water supply and an opportunity to create green jobs.
Using treated wastewater for agricultural irrigation can fertilize crops and benefit production while preventing nutrients and organic matter from entering freshwater systems. Insufficiently treated wastewater, however, can introduce pathogens, metals, excessive nutrients, POPs and emerging contaminants, and pose grave risks to workers and surrounding communities. Increased regulation, investments in treatment and risk assessments are essential for safe wastewater reuse (WHO 2006).
In West Asia, the United Arab Emirates currently reuses all treated wastewaters (290 million m3 per annum), while Saudi Arabia reuses 166 million m3. This reclaimed water is reused for agricultural production in Saudi Arabia’s Al Hassa Oasis, after being mixed with groundwater (UNEP 2016c).
Effective management considers an entire watershed or basin as a socio-ecological system integrating across agriculture, forestry, industry, domestic and commercial uses in the ecosystem context. This has improved water availability, sanitation and wastewater treatment in many countries (SDG 6.5 and 6.6) (UNEP 2016a; UNEP 2016f; UNEP 2016h). European river basin management identifies various pressures, classifies monitoring results and enforces environmental objectives (e.g. International Commission for the Protection of the Danube River 2008). There has also been substantial progress in transboundary river basin management (e.g. European Commission 1992; European Commission 2000). Furthering surface and groundwater governance requires cooperation from multinational to local levels, supported by realtime data and information management (Cross et al. 2016).
In late February 2018, Cape Town faced the prospect of ‘Day Zero’, a term coined for the date – then estimated to be 9 July – when the city was expected to run out of water, taps would run dry, and all municipal supply would be rerouted to emergency pickup points (Poplak 2018). This severe urban water scarcity in Cape Town is significant because it could have been the first major modern city to literally run out of municipal water if Day Zero was not averted by sufficient rainfall in the early winter season. There have been past cases of other cities such as Barcelona, regional capital of Catalonia, suffering its worst drought in 2008 since records began 60 years ago, with reservoirs down to a quarter of normal capacity (Keeley 2008). In 2015, Brazil’s financial capital, São Paulo, one of the world’s most populated cities (over 21.7 million inhabitants) experienced an ordeal similar to that of Cape Town when its main reservoir fell below 4 per cent capacity (Gerberg 2015).
The situation in Cape Town was caused by a three-year drought, considered to be a roughly 1-in-400-year hydrological event, resulting in the levels of the largest storage reservoir (Theewaterskloof Dam) to drop to 11 per cent of capacity (Poplak 2018). However, this proximate cause needs to be understood within a context of efforts to redress historical inequities and overcome institutional divides, and the need to innovate in the face of climate change.
Analysis of water consumption data from 400,000 households (Visser and Brühl 2018) illustrates how Capetonians rallied to avert Day Zero. Over four years of water consumption data indicate that usage by all domestic consumption brackets converged, with 63 per cent of households reaching the recommended target (under 10.5 kilolitres per month) in July 2017, and 30 per cent of households reaching the lower target of 6 kilolitres per household per month even before it came into effect in February 2018. Hence, Cape Town succeeded in halving its water consumption within three years, through a common vision and commitment by its people. A take-home message for Cape Town, and possibly for the world, is that “people’s faith in each other’s ability to safeguard the remaining water as part of a common pool resource, is critical” (Visser and Brühl 2018).
