Beyond the ocean: understanding the precise science of salt in our water

Nature · Published 3 October 2026 Swipe more like this →

In short: Salt water is more than just the ocean. Defined by the United States Geological Survey, saline water exists on a spectrum of concentration, ranging from slightly saline to highly saturated brine. By measuring parts per million, scientists categorize water based on its dissolved sodium chloride content and thermal properties.

The United States Geological Survey classifies saline water into three distinct tiers based on salt concentration. Slightly saline water contains between 1,000 and 3,000 parts per million, while moderately saline water ranges from 3,000 to 10,000 parts per million. Highly saline water reaches concentrations between 10,000 and 35,000 parts per million. For comparison, standard seawater typically sits at 35,000 parts per million, which equates to 35 grams of salt per liter of water.

The capacity of water to hold salt is surprisingly stable despite temperature fluctuations. At 20 degrees Celsius, one liter of water dissolves about 357 grams of salt, reaching a concentration of 26.3 percent by weight. Heating the water to 100 degrees Celsius allows for only a modest increase, enabling the dissolution of about 391 grams of salt, or 28.1 percent by weight. This saturation point is a fundamental physical limit, and the resulting brine exhibits unique thermal conductivity, which decreases as salinity rises but increases with higher temperatures.

Beyond its physical properties, saline water plays a critical role in industrial chemistry. Through the process of electrolysis, salt water is used to produce chlorine, with hydrogen gas generated as a significant side product. In fact, roughly four percent of the world's hydrogen supply is derived from this specific industrial pathway. Whether analyzed via a salinometer or utilized in chemical manufacturing, the interaction between water and dissolved salts remains a cornerstone of both natural systems and modern industrial efficiency.

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