Desalination is a technology that cities across the world are already implementing to help solve some of their fresh water related issues.
In this guide, we outline some of the different pros and cons of desalination technology.
Summary – Pros & Cons Of Water Desalination
It is particularly useful to regions or cities with dry and hot climates, and that have inadequate internal supplies of fresh water resources. Desalination gives these cities and regions some of the major benefits of being able to generate fresh water from salt water, diversifying their water sources, and having a water source that is independent of natural climate factors such as rainfall.
On the other hand, desalination does have some drawbacks. Desalination plants can cost millions and billions to build, and their running costs can be high because they can be energy and capital intensive, and brine disposal and management can be expensive (in some cases, they aren’t economically feasible at all from a private sector perspective). Low to moderate income cities and regions often can’t afford it, and for the ones who can, desalination can end up being one of the most expensive water sources. Additionally, they have environmental concerns when they rely on fossil fuels heavily for energy, as well as with the by-product they produce in brine (which is concentrated salt water). It can be difficult to scale desalination to a level to provide all of a region’s potable and non potable fresh water needs – for example, it may provide some portion of drinking water needs, but non potable water may still need to come from other sources.
Some water experts think that desalination is not a primary long term solution. Managing water withdrawals in the first place might be more sustainable (for regions with adequate fresh water supplies), as well as engaging with transboundary water transfers. Waste water recycling might have more long potential than desalination.
It does seem though like desalination has at least some part to play in the fresh water supply picture for several regions around the world moving forward.
A quick list of the full list of pros and cons are:
- Can make use of the biggest source of water in the world – the ocean (about 96.5% of the water on Earth’s surface is found in the ocean)
- Can make use of brackish water (in addition to ocean salt water), and other types of salt or saline water
- Can be used in coastal areas, or inland
- Removes salt, but also water pollutants
- Can prevent further contamination of other fresh water sources from existing contaminated sources
- Gives a city or town a climate independent water source that doesn’t rely on rainfall, and isn’t as affected by a dry and hot local climate
- Can help regions protect against droughts and other natural events
- Makes communities more water diverse by giving them an additional fresh water source to rely on
- Can address current critical quantity related water issues like water scarcity, water security, and water shortages. One example of a city addressing their water scarcity issues in part with water desalination technology is Perth in Western Australia. There’s also many other examples of places using desalination, with Saudi Arabia, Kuwait, Eritrea, and Qatar being just a few other examples
- Gives communities more water independence i.e. more control over their own water sources, and the ability to augment their water sources
- Can help stabilize regional, state, country and world economies – water is very important to many things we do in society
- Is predictable and consistent (as opposed to water sources that rely on natural climate and natural factors where there might be variable rainfall year to year for example)
- Is flexible and can run at partial capacity
- Can be good for cities or towns that rely on slow to recharge ground water aquifers (ground water can take up to 5 years to see a meaningful change in water levels). India is an example of a country that relies heavily on depleting ground water aquifers, particularly for agriculture and irrigation
- Water can be used in times of natural water deficits
- Creates more water for high use activities
- May reduce overall water related energy usage
- Stops water diversions
- Can produce a lot of water daily, and annually
- Good for naturally dry or hot climates
- Good for regions and countries with naturally low levels of internal fresh water resources
- Good for regions with increasing or high fresh water demand/withdrawal/consumption rates
- Plants are already widely used
- Desalination is becoming affordable and accessible on an individual level
- Brine from desalination plants has potential for re-use and can be cost effective
- Isolated or rural communities may benefit from desalination technology
- Could play a critical role in the future with forecasts estimating that water stress and scarcity could worsen in the future if current trends continue
- Could play a critical role in the future with forecasts showing that more water will be needed for a growing population, and increased water demands for food and energy
- There’s new developments, innovations and business models being worked on
- Cost to both build, and operate a desalination facility is expensive (desalination can be one of the most expensive sources of fresh water when taking into consideration building costs, energy costs, and so on. It’s certainly more expensive than sustainably managing water demand and withdrawals in the first instance)
- Low income, and underdeveloped countries are generally priced out of desalination technology
- Other water management options may be better
- Time between planning, funding approval, construction and opening/full operation can be years
- Desalination can swap a reliance on rainfall and the hydrological cycle, for a reliance on energy
- There can be various barriers to further investment and development
- Plants can cause potential contamination issues
- The brine by product that is produced can be hazardous
- The final water product can be slightly corrosive
- Good minerals can be stripped from water in the desalination process
- Desalination plants can cause pollution issues
- Desalination plants are energy intensive and require a lot of power input (energy requirements can be one of the major costs associated with running a desalination project)
- Plants that use fossil fuels contribute to climate change via GHG emissions
- Energy intensive plants can result in higher water prices
- Water input vs water output ratio can be poor
- Desalination plants can negatively impact marine life and ocean biodiversity
- Desalination plants can give people a false sense of security that water related issues will go away
- May not be a long term sustainable solution based on currently available technology (unless changes are made)
- There may be better water management solutions and strategies than desalination to try first for some cities (such as better managing withdrawals, water pricing strategies, and so on). Certainly cities with little to no natural internal fresh water resources, or cities that are situated in hot and dry climates have far more legitimate claims to desalination than cities with corrupt or incompetent water management institutions, cities that over consume and waste or lose water unnecessarily, cities that don’t responsibility or sustainably manage fresh water withdrawals, and generally manage their water supplies poorly or don’t value water as a resource.
*Desalination technology being used can differ in different parts of the world, and it is always developing with more research and investment. Also, different cities have different factors and variables to consider in using desalination technology. These variables and factors can impact the final list of pros and cons of desalination plants and water desalination technology being used in a specific area. The pros and cons listed in this guide are of a general nature only.
What Is Water Desalination & How Does It Work?
- Desalination plants can create freshwater and drinking water resources from a saltwater source, or brackish water source.
- Reverse osmosis is used in many desalination plants, which creates high-quality drinking water on small or large scales.
- Desalination is the process of removing salt and other particles from seawater and other waste water.
Types Of Water Desalination
There’s two main types of water desalination:
- Membrane, or Reverse Osmosis (sometimes referred to as pressure desalination)
- and, Thermal Desalination (MED, MVC and MSF)
Reverse osmosis is currently the leading desalination technology globally.
Read more about these technologies here (ide-tech.com)
Large.stanford.edu also mentions a third type of desalination – electrical.
In addition to the actual type of technology used for desalination facilities, different types of water can be processed, such as:
- Brackish water
- Saline water
All of these types of water contain different concentrations of total dissolved solids.
Read more about these water types here (twdb.texas.gov)
Pros Of Water Desalination & Desalination Plants
A more detailed list of the pros:
- Can Make Use Of The Biggest Source Of Water In The World – saltwater/the oceans makes up 97% of the world’s surface water, and can be utilised to create fresh water from desalination. The amount of available fresh water is much smaller, and is unequally distributed geographically all over the world – some places have a lot, while some places have little or none.
- Can Make Use Of Brackish Water & Other Types Of Water – in addition to ocean salt water, desalination plants can use brackish water and other type of water like saline water.
- Can Be Used In Coastal Areas, Or Inland – coastal desalination plants usually treat sea water. Inland desalination plants can be used to make use of brackish water and other inland water types from different water sources. Roughly one quarter of all water desalination demand is for inland brackish water desalination technology, and there’s a number of uses for inland desalination (veoliawatertechnologies.co.za). One inland desalination option is containerized desalination that can be up and running within 2 months (fluencecorp.com)
- Removes Salt, But Also Pollutants – desalination can remove contaminants from water in addition to salts. This ability allows it to treat industrial effluent as well (fluencecorp.com)
- Can Prevent Further Contamination Of Other Fresh Water Sources From Existing Brackish Water Sources – for example, a Texas desalination plant captures brackish water before it can contaminate other fresh water wells (fluencecorp.com)
- Gives Cities And Towns A Climate Independent Water Source – surface water and ground water sources are reliant on rainfall and the hydrological cycle to renew and recharge (along with other natural factors). Desalination can produce fresh water independent of these natural variables (e.g. rainfall can be variable year to year)
- Can Help Regions Protect Against Natural Events Like Droughts – droughts mean that surface water and ground water sources renew much slower, and in the case of places like Cape Town, can lead to water shortages. Desalination is largely unaffected by droughts and natural events.
- Makes Regions More Water Diverse – because a greater range of water sources can be used to produce freshwater and drinking water. There is less reliance on, and therefore less ability to be affected negatively by any one source of fresh water.
- Can Help Global Water Issues Like Water Scarcity, Water Security, & Water Shortages – as a by product of the way desalination is able to generate fresh water
- Gives Communities More Water Independence – towns or cities can rely on and control their own internal water supplies as opposed to having to rely on external water supplies and resources.
- Can Help Stabilise Economies – because water is so critical to how economies and societies work.
- Is Predictable – when a desalination plant is operational, it consistently produces a certain amount of water annually. This is compared to natural water sources that might rely on variable year to year precipitation levels, or some other unpredictable or variable water renewal factor
- Can Run At Partial Capacity (Is Flexible) – a desalination facility can run at partial capacity such as 10% if fresh water requirements are being met from other sources.
- Can Be Good For Cities Or Towns That Rely On Slow To Recharge Ground Water Aquifers – ground water aquifers are notoriously slow to recharge – with some aquifers not showing a meaningful change in water renewal levels for around 5 years or so. Slow renewal rates combined with higher withdrawals can lead to ground water depletion. Desalination eases the burden on ground water sources
- Surplus Water Supplies Can Be Used In Times Of Natural Water Deficits – while natural water supply levels are higher, a desalination plant can go into water surplus. This surplus water can be used when natural water supply levels dip.
- Creates More Water For High Use Activities – especially non potable water for activities such as irrigation and agriculture. This is only true in some instances though – sometimes, desalination only provides enough water for some drinking water needs.
- May Reduce Overall Water Related Energy Usage – current water infrastructure involves the use of pumps and other water equipment that uses energy to move and treat water (especially from some ground water sources). There’s a chance in some areas desalination plants may cause a net decrease in the total amount of water related energy used if current water infrastructure isn’t used as heavily.
- Can Stop Water Diversions – in some areas, water has to be diverted from existing sources to a new area. This can damage the ecosystem in the area where the water is being diverted away from. A desalination plant can reduce this practice.
- Can Produce A Lot Of Water – a single desalination plant like the one in Adelaide, Australia can supply 300 megalitres per day, or 100 gigalitres per annum, or 50% of a city’s drinking water needs (wikipedia.org). But, production depends on many variables – size of the plant and production capacity are just two.
- Useful For Regions With Dry & Hot Climates – like regions with high surface temperatures, or low (or variable annual) rainfall levels. Both these things impact the hydrologic cycle via precipitation, evaporation, percolation and inflow of water, and so on.
- Useful For Regions With Low Or No Internal Natural Fresh Water Resources – fresh water is not distributed evenly geographically throughout the world in the form of rivers, lakes, ground water aquifers and so on. Desalination offers a supply solution for regions with low to no internal fresh water resources.
- Useful For Regions With Increasing Or High Water Demand/Withdrawals/Consumption – demand puts strain on fresh water resources if renewal rates don’t match or exceed them, or if there isn’t abundant existing capacity of fresh water resources. Desalination can ease this demand burden.
- Already Used Widely – there are about 18,426 desalination facilities located in 150 countries worldwide with a total capacity of about 22.9 billion US gallons, based on 2017 numbers (twdb.texas.gov)
- The Salt ‘Brine’ By-Product Of Desalination Has Potential To Re-Used – some of the proposed re-uses include de-icing, injection material for deep well drilling, to be mixed with cement, and so on. Brine disposal can also be cost effective (veoliawatertechnologies.co.za)
- Isolated Or Rural Communities Can Run Desalination – and they can run it on renewable energy like solar if they stick to smaller scales of water production.
- Could Be Critical To Forecasted Water Scarcity & Stress Problems – some forecasts show water stress and other water related global issues worsening in the future in terms of the number of people affected globally. Desalination could address some of these issues.
- Could Be Critical For A Growing Water Demand In The Future – agriculture and increased food demand, increased energy demand, a growing population, a growing middle class in some countries that are still developing, and a growing demand for water intensive products like meat and fossil fuels – all point to increased demand for water in the future. Desalination could help address this increasing water demand.
- Desalination Equipment Is Becoming Affordable & Accessible On An Individual Level – Right now, a desalinator for seawater can be purchased for about $500. Some models weigh just 2.5 pounds and produces about two pints of viable water per hour. They are hand-operated, which means they can be used with a life raft, an emergency kit, and meet other needs for coastal populations.
- There’s New Developments, Innovations and Business Models Being Worked On – the wateronline.com resource in the resources list at the bottom of this guide outlines the various developments, innovations and business models being worked on to make desalination a better option.
– other sources used for these ‘pros’ include vittana.org, greengarageblog.org, brandongaille.com
Cons Of Water Desalination, & Desalination Plants
A more detailed list of the cons:
- Cost Of New Construction Is Expensive – Although several factors can dramatically change the final price of construction, a 2010 report estimated that a new desalination plant in Texas would cost $658 million to achieve 100 million gallons per day of freshwater supplies. Even at 2.5 million gallons per day, the plant would cost $32 million to build. A desalination plant in Adelaide, Australia cost A$1.83 billion to construct (wikipedia.org)
- Operational Costs Can Be High – desalination plants can be capital and energy intensive to run, which can lead to high operational costs (energy makes up a significant portion of the the running costs of some plants). In Adelaide for example – annual energy costs for their desalination facility are A$130 million (wikipedia.org). For the average desalination plant these days, it takes 2 kilowatt hours of energy in order to produce 1 cubic meter of fresh water. Though this would translate to a cost of just under 2 dollars on a lot of power grids, the real production cost comes from the expenditure of fossil fuels that are needed to create electricity for its process. Wateronline.com says that ‘brine disposal or treatment is the largest cost component of brackish and industrial water desalination’
- Other Water Management Options May Be Better For Some Regions – managing water withdrawals, implementing water pricing strategies, or engaging with other States/provinces for transboundary water transfers may be cheaper. Waste water recycling may have more long term potential. It depends on local conditions, variables and factors though, as well as future development in fresh water technology and strategy.
- Time Between Planning, Funding Approval, Construction and Operation Can Be Years – for example, the Adelaide, Australia plant took from 2008 to 2013 to go from initial funding to the plant fully opening (wikipedia.org)
- Cost Is A Barrier To Low Income & Underdeveloped Regions – some of the countries and cities that need desalination the most can’t afford it because of construction and operation costs.
- Cost Can Be A Barrier To Further Investment And Development – further R&D, and improvements to desalination technology can be expensive to finance.
- Can Swap A Reliance On Natural Factors, To A Reliance On Energy – the renewal of surface water and ground water sources rely on rainfall, the climate, catchment areas, soil, the hydrologic cycle, and many other factors. Desalination plants rely on a lot of energy to run.
- Potential For Plants To Cause Contamination Issues To Other Water Sources & The Water Supply – desalination plants can introduce certain contaminants into the local water supply and groundwater sources. Chemical, biological, or mineral contaminants can alter groundwater supplies, which would affect crop growth, water access, and potentially cause other water-related issues. To prevent this – the plant has to be monitored and the plant’s waste and discharge treatment process has to be handled properly.
- A Salt ‘Brine’ Is Produced As A By-Product Which Can Do Damage – the salt removed from saltwater, called brine, must be treated and disposed of properly. It can be naturally corrosive, and cause harm to wildlife, vegetation and sometimes individuals if not managed properly or re-used.
- The Final Water Product Can Be Corrosive – the final water product pH can be more acidic than regular natural freshwater. This water might corrode pipes and infrastructure if not filtered and treated properly.
- Good Minerals Can Be Stripped From The Water – in the purification process, bad water chemicals such as arsenic, lead, and barium can be removed. But, good minerals such as magnesium, potassium, and calcium can also be removed. Water coming from a desalination plant must be treated properly to ensure it has the right minerals if it’s used as drinking water.
- Plants Can Cause Air Pollution & Contribute To A Changing Climate – air pollutants and greenhouse gases can come from the fossil fuels burnt to make the filters, screens, and equipment for the plant, and for operation of the plant itself for energy needed (especially if coal is used). Using renewable energy to power desalination plants is an option, but renewable energy can be variable and can have other technical or practical limitations. Some plants do currently use renewable energy though.
- Plants Are Energy Intensive While In Operation, Which Can Affect Water Prices – it’s the most energy intensive water supply option that is currently available (although some ground water pumping can require a lot of energy too). In Tampa Bay, the cost of desalinated brackish water can be up to $2.60 for every 1,000 gallons of water produced. Desalinated seawater can cost up to $5.80 per 1,000 gallons of water. As mentioned above, this may be able to be minimised in the future if renewable energy develops and becomes cheaper. The average household of 4 pays about $4.50 for 100 gallons of daily water. Desalinated water access can be 25% to 75% higher. TheConversation.com outlines ‘the cost of supplying desalinated water varies widely, from $1 to $4 per kL [in Australia].
- Water Input vs Output Is Poor – for a desalination plant that is reliant on reverse osmosis, it will return as little as 5% of the water that is pushed through the system. The remaining water is often sent to the local wastewater facility for further processing and treatment. This ratio is obviously not great.
- Large Scale Water Production Requires Huge Power Input – large scale desalination plants need a lot of power, and some plants may have no choice but to use diesel.
- Large Desalination Plants Can Have A Big Toll On The Ocean & Biodiversity – The intake pipes that are used to collect water supplies for treatment can also bring in plankton, fish eggs, larvae, and microbial organisms. These are the fundamental components within the food chain that exists within the ocean. By altering the abundance of their presence, other forms of marine life become affected as well. In time, since we are at the top of this food chain, desalination even affects what seafood options are available to us. This can impact fisherman as well. In addition, if brine is dumped back in the ocean, it can cause problems.
- Some People Think Desalination Plants Are A ‘Silver Bullet’ Solution To All Water Supply Issues – this is not the case. Desalination plants have their drawbacks, and at least with current desalination technology available, they probably can’t provide unlimited fresh water forever.
– other sources used for these ‘pros’ include vittana.org, greengarageblog.org
Examples Of Water Desalination Plants Currently In Operation
- There are about 18,426 desalination facilities located in 150 countries worldwide with a total capacity of about 22.9 billion US gallons [based on 2017 numbers]
- In 2015, 53% of desalination plants were located in the Middle East, and 17% in North America
- The Tampa Bay Seawater Desalination facility, located in Florida, provides up to 25 million gallons of drinking water per day to the region.
Potential Future Of Water Desalination
- Water desalination is currently used in many locations around the world
- Having said that, water desalination needs further technological development and needs to become more affordable in the future if it’s to be used in all regions that might need it, or to be used more effectively from a private sector economics perspective
- Also, it would help to be able to operate water desalination from renewable clean energy like solar, wind and water power. Some cities already do this, but some don’t. Finding ways to consistently re-use the brine and other waste by-products would help, or being able to effectively treat, filter and dispose of them. This would help from an eco and sustainability perspective.
- There is some potential for small scale desalination in the future on an individual and small community level
- Other options to desalination like importing and transporting water between boundaries, and better managing water withdrawals and demand, may be a better options that are more affordable. Water recycling and waste water re-use may have bigger potential in the long term.
- Desalination may be one piece of the answer for future fresh water supply – it may be a supplementary or primary option heading into the future. This is especially noteworthy considering water demand is expected to increase in the future in key industries like agriculture and food production, and energy production. A growing population and the further development of developing countries has a role in this
- Each city, region and geographic area will have to assess individually if desalination is right option for them – in the short, medium and long term