Sodium is naturally present in virtually all water sources and is necessary for proper nerve and muscle function and maintaining fluid balance. However, excessive sodium intake is a concern for individuals managing conditions like hypertension, often requiring a low-sodium diet. While most daily sodium intake comes from food, the sodium in drinking water can contribute significantly, especially for those on restricted regimens. Understanding water types with minimal sodium requires knowing how the element enters the supply and what processes remove it.
Sources of Sodium in Drinking Water
Sodium enters water supplies through natural and human-related activities. The primary source is the geological environment, where groundwater passes through rock and soil, dissolving naturally occurring sodium minerals and salts. Sodium concentrations vary widely based on regional geology, ranging from less than 1 milligram per liter (mg/L) to over 250 mg/L in some areas.
Municipal water treatment processes also introduce a small amount of sodium. Chemicals used for coagulation, pH adjustment, or disinfection, such as sodium hypochlorite, contribute to the overall sodium level in the finished tap water. This contribution is generally small, often adding less than 30 mg/L, but it is a factor in the final water chemistry.
A significant source of added sodium in home tap water comes from residential water softeners using the ion-exchange method. These systems remove hardness minerals like calcium and magnesium by exchanging them for sodium ions from a salt-based resin. For every grain of hardness removed, about 8 milligrams of sodium are added per liter, meaning highly hard water can result in elevated sodium levels.
Water Types with Minimal Sodium Content
Water types reliably low in sodium have undergone specific treatment processes designed to strip out dissolved solids. Distilled water is created by boiling water into steam and then condensing it back into liquid, leaving nearly all impurities, including sodium, behind. This method results in water with a Total Dissolved Solids (TDS) content as low as 1 to 5 mg/L, making it virtually sodium-free.
Purified water is another reliable low-sodium option, often produced using reverse osmosis (RO). RO forces water through a semipermeable membrane, effectively filtering out dissolved salts and minerals like sodium. Purified water must contain no more than 10 parts per million of total dissolved solids to meet the U.S. Pharmacopeia standard, ensuring minimal sodium content.
Natural sources like spring water and mineral water are highly variable in sodium content. They acquire their mineral profiles, which can include sodium, from the underground rock and soil they flow through. Some brands of mineral water naturally contain higher sodium levels, requiring careful label reading. For those monitoring sodium intake, purified and distilled water offer the most consistent and negligible levels.
How to Determine Sodium Levels
Consumers can make informed choices by examining product labels and local water quality reports. The Food and Drug Administration (FDA) regulates bottled water labeling. Water labeled “sodium-free” or “salt-free” must contain less than 5 milligrams of sodium per serving.
A separate classification is “very low sodium,” meaning the water contains 35 milligrams or less of sodium per serving. This guidance provides a clear standard for identifying bottled water appropriate for low-sodium diets. Checking the nutritional facts panel for the actual sodium content, usually listed in milligrams, is the most direct way to confirm its level.
For municipal tap water, the sodium concentration is typically listed in the annual Consumer Confidence Report (CCR), which public water systems must provide. Since tap water sodium levels are highly regional and depend on the source water and treatment process, reviewing this report determines the local concentration. If a home uses an ion-exchange water softener, the added sodium must be calculated based on the water’s original hardness level.