Tap water contains various dissolved substances, including dissolved solids commonly referred to as “salt.” These substances are primarily in the form of ions and are present in nearly all water sources. This article explores the nature and origins of these dissolved solids, their health considerations, and methods for reducing them in your home.
What Constitutes “Salt” in Tap Water
In water chemistry, “salt” refers not just to table salt (sodium chloride), but to any ionic compound dissolved in the water. These compounds separate into positively charged cations and negatively charged anions. The total concentration of these dissolved inorganic salts and minerals is measured as Total Dissolved Solids (TDS), typically expressed in milligrams per liter (mg/L) or parts per million (ppm).
Sodium (Na+) and chloride (Cl-) are the two components of common table salt and are the primary ions of concern when discussing “saltiness” in water. High levels of these specific ions can indicate potential contamination sources. Although TDS includes other minerals like calcium, magnesium, and sulfates, sodium and chloride ions are directly responsible for the characteristic salty taste.
Where Sodium and Chloride Originate
Sodium and chloride ions enter the water supply through both natural geological processes and human activities. Naturally, water moving over and through the earth dissolves minerals from rock formations, such as ancient salt deposits and shale. This natural erosion contributes to the baseline levels of these ions found in groundwater and surface water sources.
In coastal areas, groundwater pumping can cause saltwater intrusion, where proximity to the ocean allows brackish water to seep into freshwater aquifers. Human activities often contribute the highest concentrations, particularly in urban regions. A significant source is the use of road salt (sodium chloride) for de-icing, where runoff carries the dissolved salt into water reserves.
Water treatment and waste disposal also contribute to tap water concentrations. Industrial discharge, agricultural fertilizers, and wastewater from septic systems are sources of elevated sodium and chloride levels. Additionally, many residential water softening systems exchange hardness ions for sodium ions, which increases the overall sodium content of the treated water.
Health Impact and Official Guidelines
For the average healthy adult, the sodium and chloride levels typically found in public drinking water do not pose a health risk. The majority of daily sodium intake comes from food, with drinking water usually contributing ten percent or less of the total. However, the presence of these ions becomes a concern for specific segments of the population.
The U.S. Environmental Protection Agency (EPA) recommends a sodium concentration of no more than 20 mg/L for individuals on severely restricted sodium diets (e.g., those limited to 500 mg per day). People with hypertension, kidney disease, or certain heart conditions should consult their healthcare provider about the sodium levels in their water supply.
The EPA regulates chloride under the Secondary Maximum Contaminant Levels (SMCLs), which are non-enforceable guidelines for contaminants affecting water’s aesthetic qualities. The SMCL for chloride is 250 mg/L, the concentration where most people begin to notice a salty taste. High levels of these dissolved solids can also increase water corrosivity, potentially damaging plumbing and fixtures.
Ways to Reduce Dissolved Solids at Home
For those concerned about dissolved solids, particularly sodium and chloride, certain home treatment systems are highly effective at removal.
Reverse Osmosis (RO)
The most common and effective method is a Reverse Osmosis (RO) system, which forces water through a semipermeable membrane under pressure. This membrane has extremely small pores that allow water molecules to pass through while blocking the larger dissolved salt ions, typically removing 95 to 99 percent of the TDS.
Distillation
Distillation is another reliable method, working by boiling the water and collecting the resulting steam as it condenses back into liquid. The dissolved salt ions and minerals cannot turn into gas and are left behind in the boiling chamber.
Filtration
Conversely, common water filtration pitchers and carbon block filters are generally ineffective at removing dissolved salts. Their mechanism relies on adsorption and physical straining, which cannot separate the individual ions from the water.