When water is scarce, we can’t afford to neglect the alternatives to desalination

Ian Wright, Western Sydney University and Jason Reynolds, Western Sydney University

This is the second of two articles looking at the increasing reliance of Australian cities on desalination plants to supply drinking water, with less emphasis on the alternatives of water recycling and demand management. So what is the best way forward to achieve urban water security?

An important lesson from the Millennium Drought in Australia was the power of individuals to curb their own water use. This was achieved through public education campaigns and water restrictions. It was a popular topic in the media and in daily conversations before the focus turned to desalination for water security.

Water authorities were also expanding the use of treated wastewater – often a polite term for sewage – for “non-potable” uses. These included flushing toilets, watering gardens, and washing cars and laundry.

Today, the emphasis on recycling wastewater in some locations is declining. The arguments for increased water recycling appear to be falling away now that desalinated water is available.

This trend ignores the fact that the potential supply of recycled water increases as populations grow.

Today most Australian wastewater is treated then disposed into local streams, rivers, estuaries and the ocean. In Sydney, for example, the city’s big three outfalls dump nearly 1 billion litres (1,000 megalitres, ML) a day into the ocean.

Where has recycling succeeded?

Australia has several highly successful water recycling projects.

Sydney introduced the Rouse Hill recycled water scheme in 2001. Highly treated wastewater is piped into 32,000 suburban properties in distinct purple pipes. Each property also has the normal “potable” drinking water supply.

Rouse Hill is considered a world-leading urban recycling scheme. South Australia (Mawsons Lakes) and Victoria (Yarra Valley Water, South East Water) have similar projects.

Our farmers often struggle to secure water for irrigation. Chronic water shortages across the Murray-Darling river system vividly demonstrate this.

Recycled water can play an important role in agricultural schemes. There are successful examples in South Australia (Virginia Irrigation Scheme), Victoria (Werribee) and New South Wales (Picton).

Perth has gone further by embracing water recycling for urban use with plans to treat it to a drinking water standard. Part of the extensive treatment process involves reverse osmosis, which is also used in desalination. The treated water is then pumped into groundwater aquifersand stored.

This “groundwater replenishment” adds to the groundwater that contributes about half of the city’s water supply. The Water Corporation of Perth has a long-term aim to recycle 30% of its wastewater.

Southeast Queensland, too, has developed an extensive recycled water system. The Western Corridor Recycled Water Scheme also uses reverse osmosis and can supplement drinking water supplies during droughts.

Demand management works too

Past campaigns to get people to reduce water use achieved significant results.

In Sydney, water use fell steeply under water restrictions (2003-2009). Since the restrictions have ended, consumption has increased under the softer “water wise rules”. Regional centres including (Tamworth) outside of Sydney are under significant water restrictions currently with limited relief in sight.

Despite a 25% increase in Sydney’s population, total demand for drinking water remains lower than before mandatory restrictions were introduced in late 2003.
© Sydney Water, used with permission

The Victorian government appears to be the Australian leader in encouraging urban water conservation. Across Melbourne water use per person averaged 161 litres a day over 2016-18. Victoria’s “Target 155” program, first launched in late 2008 and revived in 2016, aims for average use of 155 litres a day.

In a comparison of mainland capitals Melbourne used the least water per residential property, 25% less than the average. Southeast Queensland residents had the second-lowest use, followed by Adelaide. Sydney, Perth and Darwin had the highest use.

Although Melbourne water prices are among the highest of the major cities, lower annual water use meant the city’s households had the lowest water bills in 2016-17, analysis by the Australian Bureau of Meteorology found.

Calculated from Bureau of Meteorology data, Author provided

What impact do water prices have?

Clearly, water pricing can be an effective tool to get people to reduce demand. This could partly explain why water use is lower in some cities.

Water bills have several components. Domestic customers pay a service fee to be connected. They then pay for the volume of water they use, plus wastewater charges on top of that. Depending on where you live, you might be charged a flat rate, or a rate that increases as you use more water.

The chart below shows the pricing range in our major cities.

https://datawrapper.dwcdn.net/xIJQR/3/

Flat charges for water per kilolitre (where a kL equals 1,000 litres) apply in Sydney ($2.08/kL)), Darwin ($1.95/kL) and Hobart ($1.06/kL.

However, most water authorities charge low water users a cheaper rate, and increased prices apply for higher consumption. The most expensive water in Australia is for Canberra residents – $4.88 for each kL customers use over 50kL per quarter. The cheapest water is Hobart ($1.06/kL).

Higher fees for higher residential consumption are charged in Canberra, Perth, Southeast Queensland, across South Australia and in Melbourne. In effect, most major water providers penalise high-water-using customers. This creates an incentive to use less.

For example, Yarra Valley Water customers in Melbourne using less than 440 litres a day pay $2.64/kL. From 441-880L/day they are charged $3.11/kL. For more than 881L/day they pay $4.62/kL – 75% more than the lowest rate.

Is recycled water getting priced out of business?

Recycling water may not be viable for Sydney Water. It can cost over $5 per 1kL to produce, but the state pricing regulator, IPART, sets the cost of recycled water to Sydney customers at just under $2 per kL. That’s probably well below the cost of production.

Recycled water, where available, is a little bit more expensive ($2.12/kL) in South Australia.

Subsidies are probably essential for future large recycling schemes. This was the case for a 2017 plan to expand the Virginia Irrigation Scheme. South Australia sought 30% of the capital funding from the Commonwealth.

Where to from here?

Much of southern Australia is facing increasing water stress and capital city water supplies are falling. Expensive desalination plants are gearing up to supply more water. Will they insulate urban residents from the disruption many others are feeling in drought-affected inland and regional locations? Should we be increasing the capacity of our desalination plants?

We recommend that urban Australia should make further use of recycled water. This will also reduce the environmental impact of disposing wastewater in our rivers, estuaries and ocean. All new developments should have recycled water made available, saving our precious potable water for human consumption.

Water conservation should be given the highest priority. Pricing of water that encourages recycling and water conservation should be a national priority.

You can read the first article, on cities’ increasing reliance on desalination, here.

Ian Wright, Senior Lecturer in Environmental Science, Western Sydney University and Jason Reynolds, Research Lecturer in Geochemistry, Western Sydney University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Cities turn to desalination for water security, but at what cost?

File 20190207 174873 kcdlxk.jpg?ixlib=rb 1.1 — The largest desalination plant in Australia, Victoria’s A$3.5 billion ‘water factory’ can supply nearly a third of Melbourne’s needs.
Nils Versemann/Shutterstock

Ian Wright, Western Sydney University and Jason Reynolds, Western Sydney University

This is the first of two articles looking at the increasing reliance of Australian cities on desalination to supply drinking water, with less emphasis on alternatives such as recycling and demand management. So what is the best way forward to achieve urban water security?

Removing salts and other impurities from water is really difficult. For thousands of years people, including Aristotle, tried to make fresh water from sea water. In the 21st century, advances in desalination technology mean water authorities in Australia and worldwide can supply bountiful fresh water at the flick of a switch.

Achieving water security using desalination is now a priority for the majority of Australia’s capital cities, all but one of which are on the coast. Using the abundance of sea water as a source, this approach seeks to “climate proof” our cities’ water supplies.

It’s hard to believe now that as recently as 2004 all Australian capital city water authorities relied on surface water storage dams or groundwater for drinking water supplies. Since Perth’s first desalination plant was completed in 2006, Australian capital cities have embraced massive seawater desalination “water factories” as a way to increase water security.

Perth and Adelaide have relied most on desalination to date. Canberra, Hobart and Darwin are the only capitals without desalination.

The drought that changed everything

From the late 1990s to 2009 southeastern Australia suffered through the Millennium Drought. This was a time of widespread water stress. It changed the Australian water industry for ever.

All major water authorities saw their water storages plummet. Melbourne storages fell to as low as 25% in 2009. The Gosford-Wyong water storage, supplying a fast-growing area of more than 300,000 people on the New South Wales Central Coast, dropped to 10% capacity in 2007.

These were familiar issues in locations such as Perth, where the big dry is epic. For more than four decades, the city’s residents have been watching their supply of surface water dwindle. Remarkably, only about 10% of Perth’s water now comes from this source.

Perth’s two desalination plants have a combined output of up to 145 billion litres (gigalitres, GL) a year. That’s nearly half the city’s water needs. Both have remained in operation since they were built.

Modern industrial-scale desalination uses reverse osmosis to remove salt and other impurities from sea water. Water is forced under high pressure through a series of membranes through which salt and other impurities cannot pass.

Design, construction and maintenance costs of these industrial plants are high. They also use massive amounts of electricity, which increases greenhouse gas emissions unless renewable energy sources are used.

Another concern is the return of the excess salt to the environment. Australian studies have shown minimal impact.

Just as many of the massive new desalination factories were completed, and proudly opened by smiling politicians, it started raining. The desalination plants were switched off as storages filled. However, water consumers still had to pay for the dormant plants to be maintained – hundreds of millions of dollars a year in the case of the Melbourne and Sydney plants.

Bringing plants out of mothballs

Now drought has returned to southeast Australia. Once again, many capital city water storages are in steep decline. So what is the response of water authorities in the desal age? Not surprisingly, more desalination is their answer.

One by one the desalination plants are being switched back on. Sydney has just begun the process of restarting its plant, which was commissioned in 2010. Adelaide has plans to greatly increase the modest output from its plant this year. The Gold Coast plant, which can also supply Brisbane, is operating at a low level in “hot standby” mode.

After a dry winter, Melbourne Water is expected to advise the Victorian government to make the largest orders for desalinated water since its plant, able to produce 150GL a year, was completed in December 2012. Mothballed for more than four years, it supplied its first water to reservoirs in March 2017. The previously forecast need for 100GL in 2019-20 (annual orders are decided in April) is almost one-quarter of Melbourne’s annual demand. Plant capacity is capable of being expanded to 200GL a year.

When bushfires recently threatened Victoria’s largest water storage, the Thomson dam, the government said desalinated water could be used to replace the 150GL a year taken from the dam.

Sydney’s plan for future droughts is to double the output of its desalination plant from 250 million litres (megalitres, ML) a day to 500ML a day. This would take its contribution from 15% to 30% of Sydney’s water demand.

Perth, Adelaide, Melbourne, Brisbane and the Gold Coast already have the capacity to supply larger proportions of their populations with desalinised water as required.

What about inland and regional settlements across Australia? Large-scale desalination plants may not viable for Canberra and other inland centres. These regions would require sufficient groundwater resources and extraction may not be environmentally sound.

How much, then, do we pay for the water we use?

The plants supplying our biggest cities cost billions to construct and maintain, even when they sit idle for years.

The Australian Water Association estimates the cost of supplying desalinated water varies widely, from $1 to $4 per kL.

In fact, water costs in general vary enormously, depending on location and how much is used. The pricing structures are about as complex as mobile phone plans or health insurance policies.

The highest price is in Canberra where residents pay $4.88/kL for each kL they use over 50kL per quarter. The cheapest rate is Hobart’s $1.06/kL.

The issue of water pricing leads on to the question of what happened to the alternative strategies – recycling and demand management – that cities pursued before desalination became the favoured approach? And how do these compare to the expensive, energy-hungry process of desalination? We will consider these questions in our second article.

This article has been updated to clarify the status of advice on Melbourne’s use of desalinated water.

Ian Wright, Senior Lecturer in Environmental Science, Western Sydney University and Jason Reynolds, Research Lecturer in Geochemistry, Western Sydney University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Three reasons why it’s a bad idea to ramp up Adelaide’s desalination plant

Sarah Ann Wheeler, University of Adelaide

Drought-affected farmers in New South Wales have called for South Australia to increase the use of its desalination plant to enable an increase in water allocations for other users along the Murray River.

The farmers’ argument is that if Adelaide in particular draws less water from the river more will be available for agriculture in NSW and Victoria.

The logic may sound appealing, but there are three good reasons why it’s not a good idea. Not only is desalination an incredibly expensive project, there are other strategies – like water pricing – that can more effectively reduce water demand.

It’s also important to remember that the water flowing to South Australia is not “wasted” if it’s not diverted for industry. Stream flows are vital for keeping many ecosystems alive, and there are already serious concerns about current levels.

Adelaide doesn’t use that much water

First, Adelaide uses a very small amount of water from the River Murray. Over the past two decades, average diversions for metropolitan Adelaide and associated country areas have been just over 100 gigalitres (GL). This represents an average 1.25% of the water diversions in the Murray-Darling Basin.

SA in general (including irrigator use) has used an average 11% of water diversions over the past two decades. NSW has diverted 52% of surface water in the Murray-Darling Basin over the same period. Hence, the reality is that ramping up SA’s desal plant will have very little actual impact on NSW irrigators’ water allocations.

South Australia (the grey line) receives much less water from the Murray River than other states.
MDBA Water Audit Monitoring reports, CC BY

Desalination is expensive

Second, increasing desalination has heavy financial and environmental costs. The financial cost is why the plant has been run at only about 10% capacity (the minimum needed to maintain its working condition).

Previous economic analysis by consultants has suggested the desalination plant should only be used to increase water allocations to SA irrigators when temporary water market prices are above A$510 per megalitre (ML).

Given that temporary water prices are now trading around A$300/ML (albeit increasing due to increased water scarcity), we’re still a long way from a financial argument for turning to the desal plant, let alone considering the cost of its negative environmental impacts.

Water is always variable

Third, we need to take into account the variable nature of Australia’s irrigation sector.

Farmers in NSW are complaining that they are on zero percentages of water allocations at the start of the water year (August 1). This sounds like a big problem. But it doesn’t mean the farmers will get no water from the river at all.

At the start of the season, water managers allot water in districts to irrigators every two weeks. Depending on the type of water entitlement owned, and given the current state of water conditions (e.g. storage, inflows, rainfall predictions), water managers will allocate a percentage of water to high security entitlements first, then general security, then low security. Only in high rainfall years will the low security group get any water. Most years they get none.

Since water was separated from land in the Murray-Darling Basin, this water is not tied to any particular use. Once allocated, irrigators can use their seasonal water for their crops, store it, sell it on the water market, or even choose to let it flow down the river.

It is not unusual for irrigators with low or general security entitlements to start the water year with low or no water allocated, especially in times of water scarcity. One reason is that these rights are traditionally associated with districts where farmers typically grow annual crops like rice and cotton. They have larger farms and more water rights – but also more flexibility about the amount they plant every year.

Low water allocations at the start of the water year act as a signal to these producers to think carefully about the amount of acreage to plant in the coming months. In addition, many NSW and Victorian farmers have access to carry-over water (unused stored water from the previous year).

The other option is the water market; irrigators can enter the water market to buy water. Current temporary water prices are still historically a lot lower than prices in the Millennium Drought, when temporary prices hit over A$1000/ML in many regions.

Finally, it is important to emphasise that water destined for urban use in SA is not “wasted water” for NSW and Victoria. It is still providing surface-water flows in the basin as it makes it way to SA.

Economic studies show that a healthy and sustainable river is worth millions of dollars in tourism and recreation, plus providing important cultural values, on which many small regional town economies are heavily dependent. And there is ongoing evidence that the Murray-Darling Basin is still far from being sustainable.

Unfortunately, many of the people who support more sustainable water reallocation for the environment are widely dispersed. They often do not have the lobbying power or the resources to engage successfully in policy debate.

Of course, farmers need support. But the calls for more water to be allocated to irrigators will sound loudly as the drought continues, and it’s important to remember that there are other, less costly, options that also protect our environment.

Sarah Ann Wheeler, Professor in Water Economics, University of Adelaide

This article was originally published on The Conversation. Read the original article.

Is Perth really running out of water? Well, yes and no

File 20180213 44642 1985p1v.jpg?ixlib=rb 1.1 — The future of Perth’s urban wetlands is in doubt.
Orderinchaos/Wikimedia Commons, CC BY-SA

Don McFarlane, University of Western Australia

As Cape Town counts down to “day zero” and the prospect of its taps being turned off, there have inevitably been questions about whether the same fate might befall a major Australian city. The most striking parallels have been drawn with Perth – unsurprisingly, given its drying climate, rising evaporation rates (which increase consumption and reduce water yields) and growing population.

So is Perth really running out of water? The answer depends on what type of water is being considered, and what constitutes “running out”.

When faced with this question most people think of drinking water, which is of course essential for household use.

It often ignores non-potable groundwater that is heavily relied upon in Perth to irrigate gardens, lawns, ovals, golf courses and market gardens. This water is also used by light and heavy industry, as well as being crucial to the health of wetlands and vegetation across the coastal plain.

Lake Jualbup in Perth’s western suburbs showing periods of low and high water level. Photos by Geoffrey Dean.
saveourjewel.org, Author provided

Perth’s drinking water supplies are largely safe, thanks to early investment in the use of groundwater and in technologies such as desalination. But somewhat ironically, as this recent book chapter explains, the future supply of lower-quality water for irrigation and to support ecosystems looks far less assured.

A drying climate

Perth’s annual rainfall has been declining by about 3mm per year on average, while the number of months receiving at least 200mm of rain has halved. Meanwhile, the annual mean temperature anomaly has increased by 1℃ in southwest Western Australia in the past 40 years and possibly by more in Perth, given the urban heat island effect.

Perth’s rainfall trend, as measured at Perth Airport’s rain gauge.
Bureau of Meteorology

The overall effect is that soils and vegetation are often dry, meaning that rainfall will be lost to evapotranspiration rather than running off into rivers and dams, or recharging underground aquifers.

At the same time, Perth has made major changes to its drinking water supply. The city now relies chiefly on groundwater and desalination rather than dams. For a variety of reasons, drinking water use per person has declined, most notably since the early 2000s when sprinkler restrictions were introduced. Some have switched to self-supply sources such as backyard bores, so for them total water use may even have increased.

Perth’s trends in runoff, population, and water supply.
Water Corporation

The reduction in per capita use of drinking water is just as well, because inflows into Perth dams have fallen from 300 billion litres a year to less than 50 billion. This disproportionate drop in stream flows, even against the backdrop of declining rainfall, means that evaporation from reservoirs can exceed inflows in very dry years.

Since the late 1970s, Perth has increasingly used groundwater rather than dam water. Seawater desalination has also grown to almost half of total supply. Even more recently Perth began trialling a groundwater replenishment scheme to recharge aquifers with treated wastewater.

With the declines in rainfall and streamflow predicted to continue, water security will continue to be an important policy issue over the next few decades. Although both are much more expensive than dam water, desalination and groundwater replenishment look set to secure Perth’s drinking supply, because seawater is virtually unlimited, and wastewater availability increases in line with the city’s growth.

Why are non-drinking water supplies less secure?

Boosting drinking water supplies with desalination or groundwater replenishment is unlikely to resolve the pressures on non-potable supplies. To understand why, it is necessary to understand Perth’s unusual hydrology.

Most of Perth is built on permeable sand dunes, which can soak up even the heaviest rainfall. This allows runoff from roofs and roads to be directed into nearby soak wells and absorption basins.

As well as cheap disposal of stormwater, the sands provide Perth with a place to store excess water from winter rains, which is then relied upon for summer irrigation. As a result, local governments have been able to provide many irrigated parks and sports ovals, and more than a quarter of Perth households use a private bore to water their gardens.

This arrangement isn’t as sustainable as it once was. Groundwater levels are falling under many parts of Perth, forcing the state government to reduce allocations and to introduce a range of water-saving measures such as winter sprinkler bans.

Unlike dam inflows, we don’t yet know the full scale of the reduction in natural groundwater recharge rates. But the question still remains: what can we do to halt the decline of this important water store, particularly as Perth’s population is expected to grow to 3.5 million by 2050?

About 70% of local road runoff and half of roof runoff already recharges the shallow unconfined aquifer, because it is the cheapest way to dispose of excess water in areas with sandy soils. As well as reducing discharge costs, this practice helps to ensure that bores do not run dry in summer.

Perth also has large main drains that are designed to lower groundwater levels in swampy areas and prevent inundation. Some of these waters could be redirected into the aquifer where there is a suitable site.

Don’t waste wastewater

About 140 billion litres of treated wastewater are discharged into the ocean every year in the Perth-Peel region. A further 7 billion litres are infiltrated into the sands as a means of disposal where there isn’t an option for ocean outfall. Recent investigations of these land disposal sites have shown them to be effective in protecting wetlands from drying and providing water for public and private irrigation.

Investigations have also shown that the quality of treated wastewater can be greatly improved when infiltrated through the yellow sands into the limestone aquifer in the western part of Perth. It is suitable for irrigation after a few weeks’ residence within the aquifer.

Without these kinds of measures, local governments will struggle to water parks and sports ovals, to protect Perth’s remaining wetlands, and to safeguard the trees that help keep us cool.

So while drinking water supplies for an affluent city like Perth are reasonably secure, our vital non-drinking water supplies need to be augmented using some of the water we currently discharge into the ocean. As Perth gets even hotter and drier, and green spaces and wetlands are needed to provide much-needed cooling, we can no longer afford to let any water go to waste.

Don McFarlane, Adjunct professor, University of Western Australia

This article was originally published on The Conversation. Read the original article.

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Tag Archives for desalination

When water is scarce, we can’t afford to neglect the alternatives to desalination

Where has recycling succeeded?

Demand management works too

What impact do water prices have?

Is recycled water getting priced out of business?

Where to from here?

Cities turn to desalination for water security, but at what cost?

The drought that changed everything

Bringing plants out of mothballs

How much, then, do we pay for the water we use?

Three reasons why it’s a bad idea to ramp up Adelaide’s desalination plant

Adelaide doesn’t use that much water

Desalination is expensive

Water is always variable

Is Perth really running out of water? Well, yes and no

A drying climate

Why are non-drinking water supplies less secure?

Don’t waste wastewater

Where has recycling succeeded?

Demand management works too

What impact do water prices have?

Is recycled water getting priced out of business?

Where to from here?

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The drought that changed everything

Bringing plants out of mothballs

How much, then, do we pay for the water we use?

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Adelaide doesn’t use that much water

Desalination is expensive

Water is always variable

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A drying climate

Why are non-drinking water supplies less secure?

Don’t waste wastewater

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