Desalination: The Solution for a Sustainable Future?
Desalination: The Solution for a Sustainable Future?
Sustainability is one of the most important factors to consider when planning for the future.
In a world of growing needs and finite resources, we’re constantly searching for renewable alternatives to outdated systems.
Finding a reliable source of safe, fresh water is a vital step on the path toward a sustainable future, and desalination (or desal) is a strong candidate for being that step. Desalination is a process that produces pure, clean drinking water from the single most abundant water source on the planet: the ocean.
Desal technology has been around for literally thousands of years, and it’s a fantastic way to turn otherwise unusable water into a viable resource, so why doesn’t every coastal city in the world have a desalination plant? Unfortunately, despite the effectiveness of the process and the vast amount of desal-ready water available around the world, desalination is not a magical solution to all future water worries.
There are still limitations and drawbacks to desal plants – including the fact that clean, pure water may not actually be what we want. Is desalination a highly promising piece of the sustainability puzzle? Absolutely. Read on to find out how this technology actually works – and why we’ll still need additional systems to create a truly sustainable source of drinking water.
How does desalination work?
There are two primary types of desalination: distillation and reverse osmosis. Both are used around the world in many different forms, from small-scale personal systems to enormous desalination plants that supply water for large geographic areas.
Distillation has been used for thousands of years, as it can be performed without any complex machinery or technology. Very simply, this method involves heating up saltwater until the water evaporates, leaving the salt behind, then catching and condensing the vapour back into pure water.
This process can be done on any scale, from small solar distilleries that use the sun’s heat to catch a bowl’s worth of water, to massive distillation plants that produce thousands of cubic metres of water every day. Modern distillation plants typically use a type of thermal distillation called “multi-stage flash”, which uses vacuum chambers to boil water at lower temperatures and reuse the same brine (concentrated saltwater – the leftovers of ordinary desalination) multiple times.
Reverse osmosis is a more recent invention, requiring much more advanced technology than the sun and a few bowls. This process uses a pressure pump to force saltwater through a semi-permeable membrane with pores as small as 0.0001 microns – 700,000 times smaller than the width of a human hair.
Only pure water molecules are small enough to pass through the membrane, so reverse osmosis separates the salt from the water and leaves behind concentrated brine. This process produces quite a lot of waste, with the amount of pure water usually being significantly less than the leftover brine. Our systems, for example, produce roughly two litres of brine for every one litre of water.
Reverse osmosis has other advantages, though; no heating or cooling is required, so the process is more energy efficient than thermal distillation. It is also much easier to produce usable amounts of water quickly and at a small scale, with under-sink reverse osmosis units being an easy solution for most households to get pure filtered water out of their kitchen tap.
Why can’t we drink seawater?
It may seem like a silly question, but often we take this knowledge for granted without understanding why our bodies won’t let us drink saltwater. Why does seawater make us sick? Why does salt make us thirsty, even when it’s in water?
When saltwater gets inside our bodies, a process called osmosis – not reverse osmosis, but the regular kind – causes dehydration at the cellular level. While reverse osmosis uses a membrane to completely separate 100% water from any salt, regular osmosis attempts to make the levels equal on both sides of the membrane.
Our cells contain pure H2O, and saltwater – brace yourself for this – is a mix of water and salt. Osmosis causes our cells to lose pure water in an attempt to dilute the saltwater, while simultaneously absorbing potentially deadly amounts of salt in an attempt to achieve equilibrium. This is why our bodies reject large amounts of saltwater that enter our stomachs, forcing us to throw it up immediately.
The salt content is just one of the things in seawater that make it unsuitable for drinking without desalination. There are lots of perfectly natural but potentially harmful particles that can end up in our water, so filtration and treatment are essential no matter where your water comes from.
Who uses desalination?
Both thermal and filter desalination have been around for thousands of years, with historical records describing the Ancient Greeks boiling seawater for drinking on long voyages and Romans using clay filters to separate salt and other impurities from water.
Thermal distillation continued to be used by sailors for centuries, with evaporative desalination systems being commonly used on boats making trans-Atlantic voyages as recently as the Second World War. The first large-scale sustainable desalination plant was built in 1938 in present day Saudi Arabia. Most of the biggest desalination plants in the world are in Saudi Arabia, Israel and the United Arab Emirates.
Roughly 70% of the world’s desalinated water is used in the Middle East, but many other countries rely on this water to bolster their limited resources. Some other significant users include Lybia, Algeria and the USA (particularly Florida and California).
Desalination in Australia
Australia is a prime candidate for large-scale desalination. We are the second driest continent in the world (behind Antarctica) so we can’t rely on rainfall as our only water source, and the vast majority of our population is clustered around coastal areas and cities with easy access to seawater. Our experiments with desalination began over 100 years ago with wood-fired stills at the Coolgardie goldfields. Today, there are roughly 270 desalination plants across the country.
Our first major seawater desalination plant was commissioned in 2006 in Perth to produce 45 billion litres of water every year. Additional large-scale plants have since been built in Adelaide, Sydney, the Gold Coast and Wonthaggi Victoria, as well as a second plant near Perth. Collectively, these major plants produce more than 1.2 billion litres of clean drinking water every single day.
For people living in WA, the Water Corporation has created a handy tool that lets you see exactly where your water comes from. In Perth, for example, most of our water is either from desalination plants or groundwater stores.
Why does desalinated water still need processing?
The water produced by desalination is 100% pure – so pure that our bodies can’t actually process it. Without trace amounts of minerals, the pH level of the water drops to a level that is too acidic for our bodies.
Additionally, in large countries like Australia, water often has to travel through hundreds of kilometres of pipes before it reaches people’s homes. Bacteria and other contaminants can build up in these pipes, so chemicals like chlorine and chloramine are added to the water to neutralise bacteria and disinfect the water.
The minerals in natural water are also important for our bodies. Excess levels can cause issues with hard water, but trace amounts of calcium, magnesium, potassium and mineral salts are important for our health. Reverse osmosis removes all of these substances from your drinking water, so a post-filtration remineraliser is required to restore healthy levels of vital minerals.
The problem with desalination
Technology that allows us to turn the ocean into drinkable water may sound like the perfect solution to our concerns about water sustainability, but both distillation and reverse osmosis desalination have issues and disadvantages that prevent us from relying on them for 100% of our water.
Firstly, both methods require a significant amount of power (which, in turn, costs a significant amount of money). Thermal distillation in particular uses huge amounts of energy to heat and cool the water, without even taking into consideration the post-desalination processes.
Reverse osmosis may be less energy-intensive, but it still takes a significant amount of power to generate enough pressure to force water through the membrane. The membrane itself is also worn down over time, with any sediments or additional dissolved solids in the water accelerating the degradation process.
Small-scale reverse osmosis systems like ours may only need their membranes replaced every 6-12 months, but the membranes used in the kinds of large-scale plants that process over a million cubic metres of water every day wear out much faster and are significantly more expensive to replace.
How much is too much?
There is also the issue of the salt left behind after the process. Reverse osmosis struggles more with this problem, as the process essentially concentrates three litres of salt content into two in order to leave one litre salt-free. That remaining two litres of concentrated saltwater (known as brine) is harder to process, requiring more energy to separate the higher concentration of salt from a smaller amount of water.
Multi-stage flash desalination is able to reuse brine multiple times, but as the water becomes more concentrated, a more powerful vacuum is required to evaporate it. The power required to drop the pressure around the water increases along with the brine concentration, so the water can only be used so many times before the costs outweigh the benefits.
Regardless of the concentration levels, that brine has to end up somewhere. Reverse osmosis plants like the one in Perth simply pump the brine back into the ocean, being sure to follow strict environmental regulations to avoid impacting the surrounding ecosystem. This is the balancing act of brine concentration; desalination plants must get as much drinking water as possible out of the seawater without leaving the brine so salty that it will damage the environment.
Just one piece of the puzzle
We have yet to find a single perfect solution that will make clean, safe, sustainable drinking water available for everyone around the world, but that doesn’t mean tools like desalination don’t have significant merits. Being able to turn seawater into drinking water is a fantastic step towards water security, even if the process isn’t quite perfect.
For now, small-scale reverse osmosis is one of the best ways to guarantee that the water coming out of your tap is as pure and clean as possible. For people concerned about fluoride or heavy metals in their water, a reverse osmosis system provides next-level filtration and gives you the confidence of knowing exactly what you’re drinking.
Reverse osmosis systems are particularly effective when paired with a Complete Home filter, as the larger system removes the harsher particles and chemicals before they reach the tap, effectively doubling the lifespan of the filter membrane. In turn, the tap filter will remove anything smaller than 1 micron that slips through the larger filter, making sure you’re protected on all sides.
If you’d like to learn more about effective and affordable desalination and filtration options for your home, send us a message below or fill out our contact form.