Artificial seawater (abbreviated ASW) is a mixture of dissolved mineral salts (and sometimes vitamins) that simulates seawater. Artificial seawater is primarily used in marine biology and in marine and reef aquaria, and allows the easy preparation of media appropriate for marine organisms (including algae, bacteria, plants and animals). From a scientific perspective, artificial seawater has the advantage of reproducibility over natural seawater since it is a standardized formula. Synthetic seawater is also known as artificial seawater and substitute ocean water.
The tables below present an example of an artificial seawater (35.00‰ of salinity) preparation devised by Kester, Duedall, Connors and Pytkowicz (1967). The recipe consists of two lists of mineral salts, the first of anhydrous salts that can be weighed out, the second of hydrous salts that should be added to the artificial seawater as a solution.
|Salt||Molecular weight||g kg−1 solution|
|Sodium chloride (NaCl)||58.44||23.926|
|Sodium sulfate (Na2SO4)||142.04||4.008|
|Potassium chloride (KCl)||74.56||0.677|
|Sodium bicarbonate (NaHCO3)||84.00||0.196|
|Potassium bromide (KBr)||119.01||0.098|
|Boric acid (H3BO3)||61.83||0.026|
|Sodium fluoride (NaF)||41.99||0.003|
|Salt||Molecular weight||mol kg−1 solution|
|Magnesium chloride (MgCl2.6H2O)||203.33||0.05327|
|Calcium chloride (CaCl2.2H2O)||147.03||0.01033|
|Strontium chloride (SrCl2.6H2O)||266.64||0.00009|
While all of the compounds listed in the recipe above are inorganic, mineral salts, some artificial seawater recipes, such as Goldman and McCarthy (1978), make use of trace solutions of vitamins or organic compounds.
The International Standard for making Artificial Seawater can be found at ASTM International. The current standard is named ASTM D1141-98 (the original standard was ASTM D1141-52) and describes the standard practice for the preparation of substitute ocean water.
There are various applications for ASTM D1141-98 synthetic seawater including corrosion studies, ocean instrument calibration and chemical processing. Typically, laboratory-grade water is used when making synthetic salts 
- Kester, D. R., Duedall, I. W., Connors, D. N. and Pytkowicz, R. M. (1967). Preparation of Artificial Seawater Archived 2008-12-17 at the Wayback Machine. Limnology & Oceanography 12, 176–179.
- Goldman, J. C. and McCarthy, J. J. (1978). Steady-state growth and ammonium uptake of a fast-growing marine diatom Archived 2008-12-17 at the Wayback Machine. Limnology & Oceanography 23, 695–703.
- "Standard Practice for the Preparation of Substitute Ocean Water". ASTM International. Retrieved 16 June 2014.
- ""Artificial Seawater" ASTM D1141-98 Lake Products Company LLC".
- "Preparation of Substitute Ocean Water". G2MT Labs. 2018-11-08. Retrieved 10 November 2018.