Sodium in water: origin, effects, standards, and treatment
Sodium is a mineral naturally present in rocks, soil, and seawater. Its concentration in drinking water can increase due to saltwater intrusion, road salts, wastewater, or ion-exchange softeners. While essential to the body, it becomes a concern when total intake is excessive, particularly for people on low-sodium diets. In the European Union, the parametric value is set at 200 mg/L.
- Symbol
- Na
- Form in water
- Na+
- Main risk
- Excessive dietary intake
- EU value
- 200 mg/L
What is sodium in water?
Sodium is a chemical element with the symbol Na. In water, it is present almost exclusively as the dissolved ion Na+. Highly soluble, it usually accompanies anions such as chlorides, bicarbonates, sulfates, or nitrates.
Sodium is an essential nutrient for the body's functioning. It plays a role in water balance, nerve impulse transmission, and muscle contraction. However, excessive dietary intake contributes to elevated blood pressure and increases cardiovascular risk.
In most diets, drinking water represents only a fraction of the total daily sodium intake. It can nevertheless become a significant source in certain regions, following ion-exchange softening or for people on very low-sodium diets.
Key takeaway: sodium is generally an indicator or aesthetic parameter in drinking water. The World Health Organization does not set a specific health-based guideline value, while the European Union uses a parametric value of 200 mg/L.
Chemical properties of sodium in water
| Characteristic | Information | Importance for drinking water |
|---|---|---|
| Chemical symbol | Na | Alkali element highly reactive in metallic form. |
| Form in water | Na+ | Highly mobile dissolved ion. |
| Molar mass | 22.99 g/mol | Used for conversions between sodium and salts. |
| Solubility | Very high for many salts | Sodium is not removed by simple mechanical filtration. |
| Volatility | None in ionic form | Boiling does not remove it. |
| Charge | +1 | Allows for exchange on certain cationic resins. |
Metallic sodium does not exist in natural water because it reacts immediately with water. Analyses therefore focus on the sodium ion Na+, which is generally stable under the ordinary conditions of drinking water.
In what forms is sodium present?
Sodium is associated with various anions. The exact composition depends on the geology, marine influence, human activities, and treatments applied.
| Compound | Formula | Frequent origin |
|---|---|---|
| Sodium chloride | NaCl | Sea salt, saltwater intrusion, road salts, industrial activities. |
| Sodium bicarbonate | NaHCO3 | Dissolution of minerals and geochemical exchanges. |
| Sodium sulfate | Na2SO4 | Evaporite rocks, industrial waste. |
| Sodium nitrate | NaNO3 | Fertilizers, wastewater, agricultural activities. |
| Sodium carbonate | Na2CO3 | Water treatment, industry, alkaline geology. |
What are the natural sources of sodium?
Weathering of rocks
Sodium is released by the weathering of minerals such as feldspars and certain volcanic rocks. Water with a long contact time with geological formations can have higher concentrations.
