Water found in many homes is considered “hard” due to a high concentration of dissolved minerals, primarily calcium and magnesium. This mineral content is responsible for the chalky buildup, known as scale, that forms inside pipes, water heaters, and appliances. To combat this issue, many households install water softening systems, which treat the entire water supply. The immediate question for many consumers is whether this treated water is actually safe to drink. This article explores the science behind water softening to determine if consuming the resulting water poses health risks.
Understanding the Ion Exchange Process
Water softeners utilize a process called ion exchange to remove the problematic hardness minerals from the water supply. This system involves a tank filled with resin beads that are initially saturated with positively charged sodium ions. As hard water flows through the resin tank, the calcium and magnesium ions present in the water are chemically attracted to the resin.
The resin beads capture and hold the calcium and magnesium ions, effectively displacing the sodium ions. These released sodium ions then dissolve into the water, which is the mechanism by which the water is softened and the mineral content is altered. The result is water that is free of scale-forming minerals but contains a small, measurable amount of added sodium.
When the resin beads become saturated with calcium and magnesium, the system performs a regeneration cycle using a brine solution. This process flushes the captured hardness minerals down the drain and re-saturates the resin with a fresh supply of sodium ions for the next cycle.
Assessing the Sodium Content
The primary concern regarding the consumption of softened water is the introduction of sodium during the ion exchange process. The amount of sodium added is directly proportional to the initial hardness level of the source water. For every grain of hardness removed per gallon, approximately 7.5 milligrams (mg) of sodium are introduced.
A moderately hard water supply, around 10 grains per gallon (gpg), adds about 75 mg of sodium per gallon, translating to roughly 9.4 mg per typical 8-ounce glass. For perspective, a single slice of plain white bread often contains between 100 and 200 mg of sodium, while a cup of milk contains about 105 mg.
The United States Food and Drug Administration (FDA) recommends that healthy adults limit their sodium intake to no more than 2,300 mg per day. Drinking eight glasses of water softened from 10 gpg hardness contributes only about 75 mg of sodium to a person’s total daily intake. This minimal addition is generally considered negligible for most people.
Even in cases of extremely hard water, such as 30 gpg, the added sodium totals about 225 mg per gallon, or 28 mg per 8-ounce glass. While this is a higher concentration, it still represents a small fraction of the total daily sodium allowance.
Specific Dietary and Health Considerations
While the sodium increase is generally minor, specific populations must consider the cumulative effect of consuming softened water. Individuals on severely sodium-restricted diets, often due to conditions like hypertension, congestive heart failure, or certain kidney diseases, should exercise caution. For these patients, sodium intake must be carefully monitored, as even a small, consistent increase from drinking water could be problematic.
Another consideration involves the preparation of infant formula, particularly in homes with extremely hard source water. Infants have a lower tolerance for sodium, and excessive amounts can place undue stress on their developing systems. The concentration of sodium in the water used to mix formula should be discussed with a pediatrician or healthcare provider, especially if the source water hardness exceeds 40 gpg.
For those with medical concerns, switching to an alternative softening agent, such as potassium chloride, can alleviate the sodium concern. Potassium chloride works similarly to sodium chloride but replaces the hardness minerals with potassium ions instead of sodium ions. However, this option may not be suitable for individuals with kidney issues who also need to restrict potassium.
Alternatives for Drinking Water
For individuals who must avoid added sodium or simply prefer the taste of unsoftened water, several practical solutions exist for the drinking supply. The most straightforward approach is to install a dedicated bypass tap at the kitchen sink. This draws water from the cold water line before it enters the water softener, ensuring the water used for drinking and cooking bypasses the ion exchange process entirely, leaving it in its original, unsoftened state.
Another common strategy involves using a point-of-use filtration system on the drinking water line. Reverse osmosis (RO) systems are particularly effective because they physically filter out nearly all dissolved solids, including hardness minerals, added sodium, and other contaminants. An RO system is often installed under the kitchen sink and provides a separate faucet for highly purified drinking water.
Households that wish to soften all their water without introducing sodium can opt to use potassium chloride salt pellets for the regeneration cycle instead of the standard sodium chloride. This alternative achieves the goal of softening the water while adding potassium ions. Consumers should consult their unit’s manual to ensure compatibility before switching.