Sodium is a natural element found in water, with concentrations varying by source. It is also a constituent of food and drinking water.
Sodium’s Natural Occurrence in Water
Sodium is a widespread element, ranking as the sixth most abundant metallic ion in the Earth’s crust. Water naturally acquires sodium as it moves through geological formations. As rainfall, runoff, and groundwater interact with the Earth’s surface and subsurface, water dissolves minerals and rocks containing sodium.
This process, known as weathering, causes sodium compounds to leach from soils and rock deposits. For instance, the weathering of silicate minerals and the dissolution of evaporite deposits contribute significantly to sodium levels in natural waters. Consequently, the presence of sodium in water is often a natural characteristic rather than an indication of contamination.
Sodium Content Across Water Types
The amount of sodium in water varies considerably across different sources, influenced by factors like local geology, water treatment methods, and infrastructure. Most public water supplies typically contain less than 20 milligrams of sodium per liter (mg/L), though some regions can have levels exceeding 250 mg/L. In the United States, tap water generally contains low sodium, often below 50 mg/L, with some areas like Texas, Arizona, and California reporting higher levels, usually below 200 mg/L. Municipal water providers are often required to report sodium levels, especially if they exceed 20 mg/L. Water softeners, which use ion exchange to remove hardness minerals, can significantly increase the sodium content in tap water, sometimes to over 300 mg/L.
Sodium content in bottled water also varies widely depending on the brand and its source. Spring water typically contains very low sodium levels, generally below 20 mg/L. Conversely, mineral water can have substantially higher sodium concentrations, ranging from 100 mg/L to over 1000 mg/L. Purified bottled waters, such as those treated by reverse osmosis or distillation, tend to have very low sodium levels because these processes effectively remove most minerals.
Well water sodium levels are highly dependent on the specific underground aquifers and surrounding rock formations. Natural salt deposits, saltwater intrusion in coastal areas, and human activities like the application of road salt can all contribute to elevated sodium levels in well water. For example, a study in Maryland found average sodium levels of 92.6 mg/L in some coastal plain aquifers.
Health Implications of Waterborne Sodium
For most individuals, sodium from drinking water contributes only a small fraction (typically less than 5-10%) to their total daily intake. The majority of dietary sodium comes from food, particularly processed foods.
The amount of sodium in water can be a consideration for individuals on sodium-restricted diets, such as those managing hypertension, kidney disease, or heart failure. For these individuals, health organizations often suggest that drinking water sodium levels should not exceed 20 mg/L. Consulting a healthcare provider or checking local water quality reports and bottled water labels can help individuals determine if the sodium content in their water is suitable for their dietary needs. Water that has been softened should also be avoided for infants, as it may contain elevated sodium levels.