Issues Magazine

Water: What’s in Store?

By Greg Leslie

Access to clean water, its use on arable land and the damage it does during extreme weather are the big challenges for today’s water management.

Water shapes ecosystems, landscapes and human society; it sets the conditions under which life exists on Earth. Absence of water means absence of life.

Water’s ability to solvate a range of molecules helps the movement of minerals and nutrients essential for growth across cell walls in plants and animals. Water is less dense as a solid than as a liquid, a property vital to many aquatic ecosystems. The evaporation of water from the sea and condensation as rain, or deposition as snow or ice, is part of the process that shapes the landscape through the movement of rivers or the glaciers. As people still do today, early nomadic hunter and gatherers sought and used water sources for drinking and to cultivate crops.

These special properties of water relate to four megatrends in our management of this resource.

Delivering Adequate Fresh Water Supplies to Cities and Ecosystems

Population growth, coupled with less predictable water yield from dams and reservoirs that are replenished by rainfall, has accelerated the need to develop new sources of drinking water for cities all around the world. At the same time it is now recognised that fresh water flow is required to maintain the health of important river systems from the Mekong, Murray–Darling and Ganges. So we can’t simply dam all our rivers to ensure fresh water supply.

In the past 10 years Australians have seen how governments have moved quickly to ensure the reliability of potable water supplies for cities by developing large-scale desalination plants and water recycling schemes. These projects use a range of membrane processes that produce high quality water by removing contaminants such as dissolved salts, microorganisms and trace organics. Manufacturing potable water from water sources that are not dependent on rainfall, such as seawater and municipal wastewater, allows water authorities to accommodate population growth and manage drought.

The scale and speed of the development of the infrastructure to manufacture water has been remarkable. Between 2005 and 2012, the installed capacity of desalination water plants has grown from 45 GL to 500 GL per annum, while over the same period the volume of recycled water has grown from less than 5% to 15% of total water demand. In years to come, the development of this infrastructure to secure urban water supplies will be viewed as one of the first major responses to climate change.

The expanded use of “manufactured” water is attended by a suite of challenges. These include maintenance of the new assets to ensure the same plant life as traditional water supply infrastructure; minimising the carbon footprint of the desalination and water recycling operations; and managing the impacts of increasing power prices on the cost of manufactured water.

Plants or factories that produce manufactured water consume more electricity and carbon-intensive chemicals than conventional water treatment processes. Production of a cubic metre of water by seawater desalination requires 4 kWh of power compared with less than 0.4 kWh/m3 for a conventional plant treating water from a dam.

The long-term implication of the relatively high operating cost of manufactured water plants is significant. As the prices of electricity increase in a carbon-strained economy, the unit cost of desalinated water will increase more than the cost of alternative water supplies because of the higher sensitivity of the desalination process to power costs. For example, in the next 3 years if the average price of power in capital cities increases, as predicted, from $0.12/kWh to $0.20/kWh, the production costs of manufactured water will increase by 80% for desalination plants and by 30% for water recycling plants.

In addition, if a price of $15/tonne for carbon is set for the emissions associated with the production of the power, chemicals and membranes used in manufactured water plants, the cost of manufactured water will increase by an additional 20% and 5% for desalination and recycling plants, respectively. Consequently, water authorities will need to develop strategies to minimise energy requirements and offset the carbon footprint of desalination and water recycling plants.

Essentially, there are three options to reduce the carbon footprint of desalination and water recycling plants. These are improving the energy efficiency of the treatment process; developing or purchasing carbon credits; and reducing energy consumption associated with the use of the water in the community and industry.

While there is some scope to optimise the performance of water recycling and desalination plants, opportunities are limited to further reduce the energy requirements of the reverse osmosis membranes used to remove the dissolved salts from seawater and wastewater. The membranes used in water recycling plants operating in Australia today use only half of the power that was required in similar plants operating 10 years ago. Similarly in desalination plants, technology developments such as the use of energy recovery devices have been fully exploited and have reduced power consumption from 5.0 kWh/m3 to 3.3 kWh/m3.

The US National Academy of Sciences and the International Desalination Association have separately released reports indicating that further efforts to improve the energy efficiency of current desalination systems will yield minimal return and that a paradigm shift is required to achieve significant energy savings. While there are many active research programs, including the Australian National Centre of Excellence for Desalination recently created in Perth by the Commonwealth government, it will be several years before new techniques for desalination are available for large-scale applications.

In the short term, the carbon footprint of the large Australian desalination plants has been mostly offset by the purchase of carbon credits, generated by the production of renewable energy from wind farms. In 2009, the total renewable electricity-generating capacity of Australia’s wind farms was estimated at 1700 MW, of which 280 MW will be allocated to offset the power consumed by desalination plants that are currently in operation or under construction. Given that the entire water sector accounts for less than 4% of Australia’s total power demand, offsetting the power requirements of a few desalination plants with 16% of the credits from Australia’s wind power can be seen as a disproportionate allocation of resources.

The one area that has not been fully explored or exploited is the analysis of options to reduce the energy impact of the water sector by achieving efficiencies in the amount of energy associated with domestic use of water and the treatment of wastewater. For example, it is possible to offset the 280 MW associated with Australia’s new desalination infrastructure by replacing 1.5% of the standard domestic electric hot water heaters currently operating in Australia’s capital cities with solar hot water systems. More importantly, this approach would not lock up limited sources of renewable energy that would otherwise be available to other sectors of the community and economy. Managing the power requirements associated with the use of manufactured water would be better than offsetting the power requirements of production.

Providing Adequate Sanitation in the Developing World

The United Nations has estimated that two billion people do not have access to adequate supplies of safe drinking water. Part of this problem can be attributed to the lack of sanitation that enables the safe disposal of human waste and faeces. Pathogenic microorganisms, such as viruses and protozoa in human waste, remain viable in water. If allowed to mix with drinking water supplies or contaminate the bottles, pots and pans used to collect or store water or prepare food, they can spread through the population causing illness.

Exposure to human pathogens results in gastrointestinal illnesses. Our bodies purge the pathogens by vomiting or diarrhoea, resulting in loss of water and dehydration. Adults have sufficient body mass to endure the loss of water; however, infants and small children cannot tolerate the loss of water, and the subsequent increase in salts such as potassium and sodium in the blood can lead to organ failure. A small child exposed to contaminated water can die within 5 days.

The developed world takes the availability of clean, disinfected water and safe waste disposal for granted. However, in the West these services have been developed and refined with growing prosperity over many years. Replicating the taps and toilets of the cities and towns of developed countries in developing communities will take many years and is intractably linked to the development of their economies.

Saving the lives of children is dependent on technologies that allow water and waste to be treated in localised point-of-use systems. For example, India’s Tata Industries is pioneering small water filters manufactured from rice husks that contain nanoparticles, activated by sunlight, that disinfect water. The Gates Foundation is sponsoring the development of portable toilets that can process human waste without water or the need for expensive infrastructure to transport and treat the contaminated water. The United Nations and the World Health Organisation have implemented the WASH program to help communities develop safe practices that prevent the contamination of water supplies and cooking utensils with contaminated water.

The combined aim of these programs and initiatives is to prevent the spread of diseases and death so that communities can develop raise people out of poverty.

Arresting the Effects of Salt on Arable Land

Providing enough food to feed the seven billion people on the planet today and the eight billion people that are expected to live on the planet within the next 20 years will require innovative solutions in managing land and water resources.

The universal solvent properties of water ensure that it is an effective medium to transport nutrients to the roots of growing plants. However, water is also effective at transporting salt through the environment, which can reduce the yield of crops and destroy the structure of the soil that allows plants to take hold and grow.

Salinity of the soil can occur as more land is cleared of native vegetation to grow and cultivate food crops. The problem is complex. To grow more food, land must be cleared to make room for crops. Large established trees and other native vegetation draw on groundwater to survive, whereas crops rely on water available in the top 30–50 cm of soil. Removing the trees allows the water table to rise, bringing salts to the surface. Because crops may need more water than is locally available, water is often diverted from rivers or aquifers. This can deliver salt to the top layer of soil.

Managing this problem requires a detailed understanding of the local conditions and careful land clearing to prevent a rise in the water table. Efficient irrigation systems can avoid saturation of the soil and deliver water only to the plant roots or remove salts in situ.

Another key is research into salt-tolerant crops. Governments, research organisations and corporations are active in all of these areas.

Managing Water During Extreme Weather

Water has tremendous power to shape the environment. Fast-moving rivers and slow-moving glaciers carve paths across the surface of the Earth. Our cities are generally built in the spaces created by the action of water. Cities are designed with drains, channels, culverts and dams to manage its flow.

Traditionally, these structures were designed to handle extreme events predicted to occur once every 100 or possibly 500 years. However, these weather events have now become more unpredictable in both size and frequency. Infrastructure designed to manage the movement of rain, floods, tides and waves has in many cases proved inadequate, with tragic consequences.

In the future we will see engineers and planners develop models that better predict the impact and frequency of extreme weather events and make new efforts to redesign or relocate structures in the path of water. In other areas, cities and communities will be redesigned to better accommodate the water that is available, including more sustainable gardens and parks.

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This discussion of megatrends should be tempered by knowledge that people view trends on vastly different time scales to those of nature. The vanity of engineers and scientists lies in the belief that water can be completely harnessed and controlled. Engineers boast of structures with a 500-year design life, such as the great Hoover Dam in Nevada. This is merely a drop in the bucket of the history of water.