Potassium (K) is an essential mineral and an electrolyte that maintains fluid balance, nerve signaling, and muscle contractions, including the heart’s rhythm. Potassium is found in virtually all natural water sources. While its presence is widespread, the concentration is usually quite low, which is an important distinction when considering its overall contribution to daily intake.
How Potassium Enters the Water Supply
The presence of potassium in water begins with the natural breakdown of the Earth’s crust. Water dissolves potassium ions as it flows over and through rocks and soil containing potassium-rich minerals like feldspar and mica. This geological weathering introduces potassium into groundwater and surface water supplies, serving as the primary source of the low, ambient levels found in municipal water.
Human activities contribute additional sources, mainly through agricultural runoff. Potassium is a major component in chemical fertilizers, and excess amounts can wash from farm fields into rivers and lakes. Wastewater discharge and industrial effluents can also contain elevated levels of the mineral.
A distinct source of potassium in household water comes from certain water treatment systems. Some “salt-free” water softeners use potassium chloride instead of traditional sodium chloride to regenerate the ion exchange resin. This process replaces the hardness minerals with potassium ions, directly increasing the concentration in the treated water.
Measuring Typical Potassium Levels
The amount of potassium in drinking water is measured in milligrams per liter (mg/L), and concentrations vary widely depending on the local source and geology. In most municipal tap water systems, potassium levels are low, often ranging from less than 1 mg/L up to about 8 mg/L. This concentration is dependent on regional factors, with some areas occasionally exceeding this range.
Bottled water also shows variability based on its source, with some natural mineral waters containing a mean potassium content of approximately 3.6 mg/L. The U.S. Environmental Protection Agency (EPA) does not enforce a maximum contaminant level (MCL) for potassium in public drinking water, as it is not considered a health concern at standard concentrations. However, some non-enforceable secondary standards have been suggested, such as a level of 60 mg/L.
In areas where water softeners are used, the concentration can be dramatically higher. A water softener using potassium chloride can introduce an additional 80 mg/L or more of potassium, depending on the initial water hardness. Testing the water is often the only way to know the precise level in a home.
Health Contribution from Drinking Water
Potassium is an electrolyte necessary for the body to function correctly, with the Adequate Intake (AI) for adults set at 2,600 mg per day for women and 3,400 mg per day for men. For the vast majority of healthy people, the potassium consumed from tap water is negligible when compared to the amounts obtained from food. A balanced diet, rich in fruits, vegetables, and other unprocessed foods, provides the primary source of this mineral.
However, the potassium level in water can become a relevant concern for a specific high-risk population. Individuals with chronic kidney disease (CKD) or those taking certain medications, such as some blood pressure drugs, may have difficulty excreting excess potassium. This can lead to a condition called hyperkalemia, where potassium builds up in the blood to dangerous levels, potentially causing muscle weakness and serious heart rhythm abnormalities.
For people in this susceptible group, even a modest increase in intake from water can be meaningful. Those using potassium chloride water softeners are especially advised to consult their doctor. Medical guidance is necessary to determine if the water source needs to be changed or if a different filtration method should be used to prevent excessive consumption.
Home Filtration and Water Softening Effects
Many common home filtration systems are ineffective at removing dissolved potassium ions from the water supply. Standard pitcher filters and activated carbon block filters improve taste and remove organic contaminants like chlorine, but they do not significantly reduce the concentration of minerals, including potassium. Potassium passes through these filters because it is a small, dissolved inorganic ion.
Two water treatment methods are highly effective at removing potassium: reverse osmosis (RO) and distillation. Reverse osmosis systems use a semi-permeable membrane to filter out dissolved solids, typically removing 85% to 95% of the potassium. Distillation involves boiling the water and collecting the condensed vapor, leaving virtually all minerals behind.
Traditional softeners use sodium chloride to exchange for hardness ions, resulting in a small increase in sodium content. In contrast, softeners that use potassium chloride intentionally replace calcium and magnesium with potassium, thereby increasing the final potassium concentration in the softened water.