Many people pay a premium to enjoy water that’s been bottled for its specific mineral makeup. While it’s true that many types of high mineral content water have a distinctive, appealing taste, almost all water has at least some kind of mineral composition.
In the US, minerals most often found in the water supply include potassium, sodium, zinc, calcium, and magnesium. Research indicates that sodium and magnesium concentrations are generally higher in the west and north of the country, while midwest water has the most variable mineral content.
How do they enter the water supply?
Mostly, minerals reach our taps from groundwater, where they’re able to dissolve from aquifers into water. Generally speaking, the longer water spends underground—and the farther it travels—the higher the mineral content will be. This how some waters come to be considered ‘rare’ or more premium, given their scarcity and age.
Of course, groundwater needs to pass through a mineral-rich rock to collect these beneficial substances, meaning that some areas of the country have higher mineral-content water than others. For example, the cities of Oahu and San Jose boast tap water with mineral levels on par with many bottled water brands.
Is this about water hardness?
A map of approximate water hardness across the country, from the USGS (source: USGS).
Areas rich in calcium carbonates, such as places with limestone or dolomite bedrock, will produce water with much higher concentrations of minerals—particularly calcium and magnesium. When concentrations reach a certain point, they produce notable changes to water texture and taste. This is known as hard water.
While many people prefer the taste of hard water, high mineral content can spell bad news for household chores. Hard water can leave mineral stains on dishes and bathroom appliances, while building up inside dishwashers, laundry machines, and coffee-makers, thereby reducing efficiency. What’s more, soft water is often considered preferable for hair washing and skincare.
Most of the US runs on hard to moderately hard water. Whereas many coastal and southern states get to enjoy the benefits of softer water, Texas, Arizona, Indiana, and Utah are home to some of the hardest water in the country—with many, if not most, residents taking steps to soften their home supply.
Given the nutritional benefit of minerals such as calcium and magnesium to the body, some people consider hard water to contribute to general public health. There’s currently no conclusive evidence of the health benefits of mineral water, given how tiny mineral levels in water are. But, associations between hard water regions and lower incidences of cardiovascular disease have been identified.