Salinity is the saltiness or amount of salt dissolved in a body of water, called saline water. It is usually measured in g/L or g/kg.
Ocean thermal energy conversion (OTEC) is a renewable energy technology that harnesses the temperature difference between the warm surface waters of the ocean and the cold depths to run a heat engine to produce electricity. It is a unique form of clean energy generation that has the potential to provide a consistent and sustainable source of power. Although it has challenges to overcome, OTEC has the potential to provide a consistent and sustainable source of clean energy, particularly in tropical regions with access to deep ocean water.
Distilled water is water that has been boiled into vapor and condensed back into liquid in a separate container. Impurities in the original water that do not boil below or near the boiling point of water remain in the original container. Thus, distilled water is a type of purified water.
Desalination is a process that takes away mineral components from saline water. More generally, desalination is the removal of salts and minerals from a target substance, as in soil desalination, which is an issue for agriculture. Saltwater is desalinated to produce water suitable for human consumption or irrigation. The by-product of the desalination process is brine. Desalination is used on many seagoing ships and submarines. Most of the modern interest in desalination is focused on cost-effective provision of fresh water for human use. Along with recycled wastewater, it is one of the few rainfall-independent water resources.
A hydrometer or lactometer is an instrument used for measuring density or relative density of liquids based on the concept of buoyancy. They are typically calibrated and graduated with one or more scales such as specific gravity.
Seawater, or sea water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5%. This means that every kilogram of seawater has approximately 35 grams (1.2 oz) of dissolved salts. The average density at the surface is 1.025 kg/L. Seawater is denser than both fresh water and pure water because the dissolved salts increase the mass by a larger proportion than the volume. The freezing point of seawater decreases as salt concentration increases. At typical salinity, it freezes at about −2 °C (28 °F). The coldest seawater still in the liquid state ever recorded was found in 2010, in a stream under an Antarctic glacier: the measured temperature was −2.6 °C (27.3 °F).
A salt lake or saline lake is a landlocked body of water that has a concentration of salts and other dissolved minerals significantly higher than most lakes. In some cases, salt lakes have a higher concentration of salt than sea water; such lakes can also be termed hypersaline lakes, and may also be pink lakes on account of their colour. An alkalic salt lake that has a high content of carbonate is sometimes termed a soda lake.
Saline water is water that contains a high concentration of dissolved salts. On the United States Geological Survey (USGS) salinity scale, saline water is saltier than brackish water, but less salty than brine. The salt concentration is usually expressed in parts per thousand and parts per million (ppm). The USGS salinity scale defines three levels of saline water. The salt concentration in slightly saline water is 1,000 to 3,000 ppm (0.1–0.3%); in moderately saline water is 3,000 to 10,000 ppm (0.3–1%); and in highly saline water is 10,000 to 35,000 ppm (1–3.5%). Seawater has a salinity of roughly 35,000 ppm, equivalent to 35 grams of salt per one liter of water. The saturation level is only nominally dependent on the temperature of the water. At 20 °C (68 °F) one liter of water can dissolve about 357 grams of salt, a concentration of 26.3 percent by weight. At 100 °C (212 °F), the amount of salt that can be dissolved in one liter of water increases to about 391 grams, a concentration of 28.1% w/w.
Osmotic power, salinity gradient power or blue energy is the energy available from the difference in the salt concentration between seawater and river water. Two practical methods for this are reverse electrodialysis (RED) and pressure retarded osmosis (PRO). Both processes rely on osmosis with membranes. The key waste product is brackish water. This byproduct is the result of natural forces that are being harnessed: the flow of fresh water into seas that are made up of salt water.
Total dissolved solids (TDS) is a measure of the dissolved combined content of all inorganic and organic substances present in a liquid in molecular, ionized, or micro-granular suspended form. TDS are often measured in parts per million (ppm). TDS in water can be measured using a digital meter.
An evaporator is a type of heat exchanger device that facilitates evaporation by utilizing conductive and convective heat transfer, which provides the necessary thermal energy for phase transition from liquid to vapor. Within evaporators, a circulating liquid is exposed to an atmospheric or reduced pressure environment, causing it to boil at a lower temperature compared to normal atmospheric boiling.
Aquarius was a NASA instrument aboard the Argentine SAC-D spacecraft. Its mission was to measure global sea surface salinity to better predict future climate conditions.
An electrical conductivity meter measures the electrical conductivity in a solution. It has multiple applications in research and engineering, with common usage in hydroponics, aquaculture, aquaponics, and freshwater systems to monitor the amount of nutrients, salts or impurities in the water.
Reverse osmosis (RO) is a water purification process that uses a semi-permeable membrane to separate water molecules from other substances. RO applies pressure to overcome osmotic pressure that favors even distributions. RO can remove dissolved or suspended chemical species as well as biological substances, and is used in industrial processes and the production of potable water. RO retains the solute on the pressurized side of the membrane and the purified solvent passes to the other side. It relies on the relative sizes of the various molecules to decide what passes through. "Selective" membranes reject large molecules, while accepting smaller molecules.
Conductivity or specific conductance of an electrolyte solution is a measure of its ability to conduct electricity. The SI unit of conductivity is siemens per meter (S/m).
The following outline is provided as an overview of and topical guide to water:
The Chaplin's patent distilling apparatus with Steam pump for circulating water attached was an early design of an evaporator, a device for producing fresh water on board ship by distillation of seawater. An example of this apparatus has been recovered from the wreck of SS Xantho (1872), an auxiliary steamship used in Australia to transport passengers and trade goods before ultimately sinking in Port Gregory, Western Australia in 1872. It is purported that the Alexander Chaplin distiller from the Xantho wreck is the only known surviving example of a Chaplin distilling apparatus on board a vessel of this period.
An evaporator, distiller or distilling apparatus is a piece of ship's equipment used to produce fresh drinking water from sea water by distillation. As fresh water is bulky, may spoil in storage, and is an essential supply for any long voyage, the ability to produce more fresh water in mid-ocean is important for any ship.
A distilling ship is a class of military ships, generally converted tankers, with the capability to convert salt water into fresh water. They were typically stationed at forward bases during conflict where they supported on-the-ground troops and front line naval units.
An anchialine system is a landlocked body of water with a subterranean connection to the ocean. Depending on its formation, these systems can exist in one of two primary forms: pools or caves. The primary differentiating characteristics between pools and caves is the availability of light; cave systems are generally aphotic while pools are euphotic. The difference in light availability has a large influence on the biology of a given system. Anchialine systems are a feature of coastal aquifers which are density stratified, with water near the surface being fresh or brackish, and saline water intruding from the coast at depth. Depending on the site, it is sometimes possible to access the deeper saline water directly in the anchialine pool, or sometimes it may be accessible by cave diving.
