The World Water Development Report (WWDR) is released annually, to coincide with World Water Day, and provides an annual assessment of the world’s freshwater resources. The 2018 report suggests that global demand for water will continue to increase to 2050. It also emphasises that nature-based solutions to water resource management challenges, including the purification and storage of water, could help to ensure that the global water supply is capable of meeting the world’s future water requirements.
Global water consumption increased six-fold over the past century. Currently an estimated 4,600 cubic kilometres of water is used by global agriculture, industry and households each year. Global demand for water is expected to rise at about one per cent per year until 2050, mainly due to population growth and economic development. The increased pollution of water bodies is also predicted to simultaneously reduce the available global supply of clean water.
By 2050, 4.8-5.7 billion people could live in areas of the world that are water-scarce for at least one month per year; currently, 3.6 billion people already live in that condition. The adoption of “nature-based solutions” that make greater use of natural processes to manage water resources, is one way of reducing the water stress that will accompany population growth. The WWDR explains that relying on “grey infrastructure”, which includes built infrastructure, such as dams and canals, will not solve all the global water challenges of the 21st century. The report does not advocate the replacement of grey infrastructure; instead it suggests that simply building new infrastructure to meet increased demand for water is not always the most appropriate, or cost effective, method of managing water.
Turning to groundwater supplies or building dams, both of which were common policy solutions to water scarcity in the past, are not credible options in many instances, as one-third of the world’s aquifers are already stressed and the most viable sites for dams have already been used.
The WWDR draws attention to the role of ecosystems in water resource management. It notes that most of the world’s soil resources are in fair, poor or very poor condition, which has negative implications for the cycling of water and for agricultural production. Degraded soil increases evaporation rates, lowers water retention and results in greater surface runoff, which contributes to higher rates of soil erosion and water pollution.
To improve soil conditions, the WWDR advocates the wider adoption of conservation agriculture, which incorporates three basic principles: minimum soil disturbance, greater soil cover and regular crop rotation. The amount of cropland managed according to the principles of conservation agriculture has tripled since the 1990s, but represents only slightly more than one per cent of the world’s cropland. Expanding the proportion of cropland managed according to the conservation principles would limit emissions of nitrates and phosphorus into the environment, thereby reducing the cost of water treatment.
As the 2017 WWDR argued, wastewater is a largely untapped resource. About 80 per cent of the world’s industrial and municipal wastewater is discharged into the environment without adequate treatment. Filtering treated wastewater through the subsurface – via a process known as “soil aquifer treatment” – can further improve water quality. Treated wastewater is pumped into a depleted aquifer to replenish the groundwater supply and to store water for later use. When the water is required, it is pumped to the surface, treated to drinking water quality and added to the water supply network. The Water Corporation in Western Australia is already using this process to create another climate-independent source of water, in addition to desalination plants. Similarly, parts of California have used managed aquifer recharge techniques to pump recycled water into natural aquifers for more than 75 years.
Nature-based solutions to water resource management have been utilised in various parts of the world for decades. Those solutions are likely to become more widely accepted as global demand for water increases; the alternative is to live in a more water stressed world.