Editing Desalination (section)

==Design aspects==

===Energy consumption===
The desalination process's energy consumption depends on the water's salinity. [[Brackish water]] desalination requires less energy than [[seawater]] desalination.<ref name="Panagopoulos2020">{{Cite journal|last=Panagopoulos|first=Argyris|date=2020-12-01|title=A comparative study on minimum and actual energy consumption for the treatment of desalination brine|url=http://www.sciencedirect.com/science/article/pii/S0360544220318405|journal=Energy|language=en|volume=212|pages=118733|doi=10.1016/j.energy.2020.118733|bibcode=2020Ene...21218733P |s2cid=224872161|issn=0360-5442}}</ref>

The energy intensity of seawater desalination has improved: It is now about 3 kWh/m<sup>3</sup> (in 2018), down by a factor of 10 from 20-30 kWh/m<sup>3</sup> in 1970.<ref name="IWA2022" />{{rp|24}} This is similar to the energy consumption of other freshwater supplies transported over large distances,<ref>Wilkinson, Robert C. (March 2007) [http://www.westbasin.org/files/general-pdfs/Energy--UCSB-energy-study.pdf "Analysis of the Energy Intensity of Water Supplies for West Basin Municipal Water District"] {{webarchive|url=https://web.archive.org/web/20121220210850/http://www.westbasin.org/files/general-pdfs/Energy--UCSB-energy-study.pdf |date=December 20, 2012 }}, Table on p. 4</ref> but much higher than local fresh [[water supply|water supplies]] that use 0.2 kWh/m<sup>3</sup> or less.<ref>[http://www.circleofblue.org/waternews/wp-content/uploads/2010/08/EPRI-Volume-4.pdf "U.S. Electricity Consumption for Water Supply & Treatment"] {{webarchive|url=https://web.archive.org/web/20130617040130/http://www.circleofblue.org/waternews/wp-content/uploads/2010/08/EPRI-Volume-4.pdf |date=June 17, 2013 }}, pp. 1–4 Table 1-1, Electric Power Research Institute (EPRI) Water & Sustainability (Volume 4), 2000</ref>

A minimum energy consumption for seawater desalination of around 1 kWh/m<sup>3</sup> has been determined,<ref name="Panagopoulos2020" /><ref>Elimelech, Menachem (2012) [http://www.nwri-usa.org/documents/Elimelech_000.pdf "Seawater Desalination"] {{Webarchive|url=https://web.archive.org/web/20140223110451/http://www.nwri-usa.org/documents/Elimelech_000.pdf |date=February 23, 2014 }}, p. 12 ff</ref><ref>{{Cite journal | doi = 10.1021/es801330u| pmid = 19068794| title = Energy Issues in Desalination Processes| journal = Environmental Science & Technology| volume = 42| issue = 22| pages = 8193–201| year = 2008| last1 = Semiat | first1 = R. |bibcode = 2008EnST...42.8193S }}</ref> excluding prefiltering and intake/outfall pumping. Under 2 kWh/m<sup>3</sup><ref>[http://www.usbr.gov/research/AWT/reportpdfs/ADC_SWRO_DA.pdf "Optimizing Lower Energy Seawater Desalination"] {{Webarchive|url=https://web.archive.org/web/20150618132743/http://www.usbr.gov/research/AWT/reportpdfs/ADC_SWRO_DA.pdf |date=2015-06-18 }}, p. 6 figure 1.2, Stephen Dundorf at the IDA World Congress November 2009</ref> has been achieved with [[reverse osmosis]] membrane technology, leaving limited scope for further energy reductions as the [[reverse osmosis]] energy consumption in the [[1970s]] was 16 kWh/m<sup>3</sup>.<ref name="Panagopoulos2020" />

Supplying all US domestic water by desalination would increase domestic [[Energy in the United States|energy consumption]] by around 10%, about the amount of energy used by domestic refrigerators.<ref>[http://www.amtaorg.com/wp-content/uploads/7_MembraneDesalinationPowerUsagePutInPerspective.pdf "Membrane Desalination Power Usage Put In Perspective" ] {{Webarchive|url=https://web.archive.org/web/20140424044855/http://www.amtaorg.com/wp-content/uploads/7_MembraneDesalinationPowerUsagePutInPerspective.pdf |date=April 24, 2014 }}, American Membrane Technology Association (AMTA) April 2009</ref> Domestic consumption is a relatively small fraction of the total water usage.<ref>[http://water.usgs.gov/edu/wateruse-total.html] Total Water Use in the United States</ref>

{| class="wikitable sortable wiki table"
|+ Energy consumption of seawater desalination methods (kWh/m<sup>3</sup>)<ref>[http://www.desware.net/Energy-Requirements-Desalination-Processes.aspx "Energy Requirements of Desalination Processes"], ''Encyclopedia of Desalination and Water Resources'' (DESWARE). Retrieved June 24, 2013</ref>
|- style="line-height:120%;"
! Desalination Method   ⇨
! rowspan="2" | [[Multi-stage flash distillation|Multi-stage<br>Flash<br>"MSF"]]
! rowspan="2" | [[Multiple-effect distillation|Multi-Effect<br>Distillation<br>"MED"]]
! rowspan="2" | [[Vapor-compression desalination|Mechanical Vapor<br>Compression<br>"MVC"]]
! rowspan="2" | [[Reverse osmosis|Reverse<br>Osmosis<br>"RO"]]
|- style="line-height:120%;"
! Energy ⇩
|-
| Electrical energy || 4–6 || 1.5–2.5 || 7–12 || 3–5.5
|-
| Thermal energy || 50–110 || 60–110 || ''none'' || ''none''
|-
| Electrical equivalent of thermal energy || 9.5–19.5 || 5–8.5 || ''none'' || ''none''
|-
| Total equivalent electrical energy || 13.5–25.5 || 6.5–11 || 7–12 || 3–5.5
|}
Note: "Electrical equivalent" refers to the amount of electrical energy that could be generated using a given quantity of thermal energy and an appropriate turbine generator. These calculations do not include the energy required to construct or refurbish items consumed.

Given the energy-intensive nature of desalination and the associated economic and environmental costs, desalination is generally considered a last resort after [[water conservation]]. But this is changing as prices continue to fall.

===Cogeneration===
[[Cogeneration]] is generating useful heat energy and electricity from a single process. Cogeneration can provide usable heat for desalination in an integrated, or "dual-purpose", facility where a power plant provides the energy for desalination. Alternatively, the facility's energy production may be dedicated to the production of potable water (a stand-alone facility), or excess energy may be produced and incorporated into the energy grid. Cogeneration takes various forms, and theoretically any form of energy production could be used. However, the majority of current and planned cogeneration desalination plants use either [[fossil fuels]] or [[nuclear power]] as their source of energy. Most plants are located in the Middle East or North Africa, which use their petroleum resources to offset limited water resources. The advantage of dual-purpose facilities is they can be more efficient in energy consumption, thus making desalination more viable.<ref>{{Cite journal | doi = 10.1016/j.desal.2005.03.095| title = Overview of hybrid desalination systems – current status and future prospects| journal = Desalination| volume = 186| issue = 1–3| page = 207| year = 2005| last1 = Hamed | first1 = O. A. | bibcode = 2005Desal.186..207H| citeseerx = 10.1.1.514.4201}}</ref><ref>{{Cite journal | doi = 10.1016/j.desal.2004.06.053| title = The role of nuclear desalination in meeting the potable water needs in water scarce areas in the next decades| journal = Desalination| volume = 166| page = 1| year = 2004| last1 = Misra | first1 = B. M. | last2 = Kupitz | first2 = J.| bibcode = 2004Desal.166....1M}}</ref>

[[File:Shevchenko BN350 desalinati.jpg|thumb|right|upright=1.25|The [[BN-350 reactor|Shevchenko BN-350]], a former nuclear-heated desalination unit in Kazakhstan]]
The current trend in dual-purpose facilities is hybrid configurations, in which the permeate from reverse osmosis desalination is mixed with distillate from thermal desalination. Basically, two or more desalination processes are combined along with power production. Such facilities have been implemented in Saudi Arabia at [[Jeddah]] and [[Yanbu]].<ref>{{Cite journal | doi = 10.1016/S0011-9164(04)00151-1| title = Hybrid systems in seawater desalination – practical design aspects, present status and development perspectives| journal = Desalination| volume = 164| page = 1| year = 2004| last1 = Ludwig | first1 = H. | issue = 1| bibcode = 2004Desal.164....1L}}</ref>

A typical [[supercarrier]] in the US military is capable of using nuclear power to desalinate {{convert|1500000|L|abbr=on}} of water per day.<ref>Tom Harris (August 29, 2002) [http://science.howstuffworks.com/aircraft-carrier2.htm How Aircraft Carriers Work]. Howstuffworks.com. Retrieved May 29, 2011.</ref>

===Alternatives to desalination===
Increased [[water conservation]] and efficiency remain the most cost-effective approaches in areas with a large potential to improve the efficiency of water use practices.<ref>[[Peter Gleick|Gleick, Peter H.]], Dana Haasz, Christine Henges-Jeck, Veena Srinivasan, Gary Wolff, Katherine Kao Cushing, and Amardip Mann. (November 2003.) [http://www.pacinst.org/reports/urban_usage/waste_not_want_not_full_report.pdf "Waste not, want not: The potential for urban water conservation in California."] (Website). ''[[Pacific Institute]]''. Retrieved September 20, 2007.</ref> Wastewater reclamation provides multiple benefits over desalination of saline water,<ref>Cooley, Heather, [[Peter Gleick|Peter H. Gleick]], and Gary Wolff. (June 2006.) ''[[Pacific Institute]]''. Retrieved September 20, 2007.</ref> although it typically uses desalination membranes.<ref name="50years">{{cite journal | last=Warsinger | first=David | title=Desalination Innovations Needed to Ensure Clean Water for the Next 50 Years | journal=The Bridge | publisher=National Academy of Engineering | volume=50 (S) | year=2020 }}</ref> [[Urban runoff]] and storm water capture also provide benefits in treating, restoring and recharging groundwater.<ref>[[Peter Gleick|Gleick, Peter H.]], Heather Cooley, David Groves (September 2005). [http://pacinst.org/reports/california_water_2030/ca_water_2030.pdf "California water 2030: An efficient future."]. ''[[Pacific Institute]]''. Retrieved September 20, 2007.</ref>

A proposed alternative to desalination in the American Southwest is the commercial importation of bulk water from water-rich areas either by [[oil tanker]]s converted to water carriers, or pipelines. The idea is politically unpopular in Canada, where governments imposed trade barriers to bulk water exports as a result of a [[North American Free Trade Agreement]] (NAFTA) claim.<ref>[http://www.sunbeltwater.com/docs.shtml Sun Belt Inc. Legal Documents]. Sunbeltwater.com. Retrieved May 29, 2011.</ref>

The [[California Department of Water Resources]] and the [[California State Water Resources Control Board]] submitted a report to the state legislature recommending that urban water suppliers achieve an indoor water use efficiency standard of {{convert|55|USgal|L|abbr=off}} per capita per day by 2023, declining to {{convert|47|USgal|L|abbr=off}} per day by 2025, and {{convert|42|USgal|L|abbr=off}} by 2030 and beyond.<ref>State Agencies Recommend Indoor Residential Water Use Standard to Legislature, California Department of Water Resources, November 30, 2021, [https://water.ca.gov/News/News-Releases/2021/Nov-21/State-Agencies-Recommend-Indoor-Residential-Water-Use-Standard Original], [https://web.archive.org/web/20211202140532/https://water.ca.gov/News/News-Releases/2021/Nov-21/State-Agencies-Recommend-Indoor-Residential-Water-Use-Standard Archive]</ref><ref>[https://www.sacbee.com/news/california/water-and-drought/article239028703.html Myth about huge California fines for shower and laundry usage won't die. Here's what's true], The Sacramento Bee, January 8, 2020</ref><ref>[https://www.cbsnews.com/news/marin-county-california-water-restrictions-drought/ Some in California have to limit their daily water usage to 55 gallons. Here's what that means for everyday activities], CBS News, December 8, 2021</ref>