Understanding Purified Water and Its Purity
Purified water is water that has been mechanically filtered or processed to remove impurities and contaminants. These can include a wide range of substances, from chemicals and heavy metals to dissolved solids like salt. The key to whether salt is present lies entirely in the specific method of purification used, as some techniques are designed to remove dissolved minerals while others are not. For instance, a basic activated carbon filter can remove chlorine and improve taste but will have no effect on sodium levels. On the other hand, more advanced methods are highly effective at producing water that is nearly free of dissolved salts.
How Salt is Removed from Water
Different purification technologies target different types of contaminants. To get water that has little to no salt content, you need to use methods that specifically remove dissolved mineral ions.
Reverse Osmosis (RO)
Reverse osmosis is one of the most effective methods for removing dissolved solids, including salt, from water. It works by forcing water through a semipermeable membrane under high pressure. The membrane has microscopic pores that allow water molecules to pass through but block larger molecules and ions, such as sodium and chloride. RO systems can remove up to 99% of sodium, making them the gold standard for reducing salt in residential drinking water.
Distillation
Distillation mimics the natural hydrologic cycle by boiling water and then condensing the steam back into a liquid in a separate container. Since salt and other minerals do not evaporate with the water, they are left behind in the boiling vessel, resulting in extremely pure, salt-free water. While effective, this process is generally slower and more energy-intensive than reverse osmosis for large volumes.
Deionization (DI)
Deionization systems use ion-exchange resins to remove mineral ions like sodium, calcium, and magnesium. Water is passed through tanks containing these resins, which exchange the undesirable ions for hydrogen and hydroxide ions. These then combine to form pure water (H2O). For drinking, DI water often requires a remineralization stage to restore beneficial minerals and improve taste, but this remineralization typically does not reintroduce sodium.
What About Other Water Sources?
It is crucial to understand the difference between purified water and other common water types to assess their salt content.
Standard Filtered Water
Common household pitcher filters and faucet attachments that use activated carbon or sediment filtration are not designed to remove dissolved salts. These filters are excellent for improving taste, removing chlorine, and trapping larger particles, but they will not change the sodium concentration of the water.
Water Softened Water
Traditional ion-exchange water softeners work by replacing hard minerals (calcium and magnesium) with sodium ions. This process actually increases the sodium content of the water, and the amount of sodium added can be significant depending on the initial hardness of the water supply. People on sodium-restricted diets are typically advised to drink unsoftened water or use a separate RO system for their drinking water.
Boiling Water
Boiling water at home is a method of disinfection that kills bacteria and viruses but has the opposite effect on dissolved solids like salt. As water evaporates during boiling, the salt is left behind, becoming more concentrated in the remaining water. Therefore, boiling water is not an effective way to remove salt.
Why Minimal Salt in Water Matters
For most healthy adults, the small amount of sodium in drinking water does not significantly impact their overall dietary intake. However, for individuals on sodium-restricted diets due to conditions like hypertension, heart disease, or kidney problems, the sodium from water can be a concern. The recommended intake of sodium on a very strict diet is typically low, and even small amounts from water can add up throughout the day. For these individuals, a reliable low-sodium water source is essential. The Environmental Protection Agency (EPA) suggests a guideline of less than 60 ppm (mg/L) for sodium for aesthetic reasons, but medical guidelines for restricted diets are much stricter.
Water Purity and Salt Content Comparison
| Water Type | Purification Method | Effective at Removing Salt? | Typical Sodium Range (mg/L) | Notes |
|---|---|---|---|---|
| Tap Water (U.S. Average) | Municipal Treatment | No | 5–20 | Varies by location; higher in some areas. |
| Purified (Reverse Osmosis) | Reverse Osmosis | Yes | <1 to 5 | Removes 95–99% of dissolved salts. |
| Purified (Distillation) | Distillation | Yes | <1 | Extremely low sodium due to boiling process. |
| Water Softened | Ion Exchange | No | 20–300+ | Adds sodium; depends on water hardness. |
| Standard Filtered | Carbon/Sediment Filtration | No | No change | Does not remove dissolved salts. |
Conclusion: Choosing the Right Water for You
In conclusion, the presence of salt in purified water is not a simple 'yes' or 'no' answer, but rather depends on the method of purification. While some advanced systems like reverse osmosis, distillation, and deionization can produce water with negligible sodium content, common filters and water softeners do not. For most people, the trace amounts of sodium in tap water are not a health concern, but for those on sodium-restricted diets, selecting a correctly purified water source is critical. Understanding these differences empowers you to make informed decisions for your health and hydration. For more specific health guidance regarding sodium intake, consulting a healthcare provider is recommended. A reliable source for general health guidelines is the CDC website.
Note: Some bottled waters labeled as 'purified' may have small amounts of added minerals for taste, so it is always wise to check the label.
