Understanding salinity in drinking water

Jan. 22, 2015

BIRMINGHAM — In Water Technology’s January issue, Technical Editor Dr. Joseph Cotruvo writes about salinity.

BIRMINGHAM — In Water Technology’s January Professor POU/POE, Technical Editor Dr. Joseph Cotruvo writes about salinity in drinking water.

In the article, Cotruvo explains that a significant component of the quality of drinking water is salinity (dissolved solids), which can be beneficial or harmful, as well as aesthetically pleasing or a reason for rejection of the water.

He states, “Distilled water, desalinated water and rainwater have minimal salt content. Seawater and brines have tens of thousands of parts per million (ppm) of salts, and typical drinking waters can have hundreds to well over 1,000 ppm, mostly less than 200 ppm concentration (ppm equals milligrams per liter of water). The problems are: How much is too much salinity? What are aesthetic issues? Are there any potential health consequences, and can it be managed at a reasonable cost?”

Cotruvo reports more than 97 percent of Earth’s water is salt water, and natural water’s salinity can range from very low levels from rain to less than 100 mg/l in several fresh water sources, to around 35,000 ppm in oceans and over 50,000 ppm of total dissolved solids in certain costal and confined seawaters.

Also discussed in the article are salinity standards in drinking water. Cotruvo explains that some individual ions, such as borate or lead, have sufficient toxicity resulting in health-based standards or guidelines for drinking water. However, he continues, “most of the mass of salinity in water” contains only aesthetic concerns with recommended values like total dissolved solids (TDS) or hardness, and there are Secondary Maximum Contaminant Levels (SMCLs) in the U.S. based on taste or other aesthetic reasons.

According to Cotruvo, humans can tolerate limited amounts of salts in water “for reasons of health and palatability,” but cannot tolerate excess salt intake. He notes in the article that there are also indications of positive benefits of minerals like magnesium and calcium in drinking water.

When it comes to treating salt in water, “The universal treatment for salinity is membrane treatment related to desalination. Nanofiltration membranes are capable of removing multivalent ions more efficiently than monovalent ions, so they can be somewhat effective especially in non-seawaters,” says Cotruvo in the article. “Reverse osmosis achieves removal in the [98 to 99] percent range in thousands of high pressure seawater desalination applications that can operate at rates as high as multimillion gallons per day.”

You can find the entire January Professor POU/POE on salinity in drinking water here.

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