Water Hardness
CaCO₃·Affects skin,
Hardness is the calcium and magnesium dissolved in your water, measured as calcium carbonate equivalent. The EPA does not regulate it, but it is the single most common reason people call us: scale buildup, soap scum, dry skin, and shortened appliance life all trace back to it.
CaCO₃
EPA limit
No EPA standard
Most at risk
Almost every US household. Hardness is the most widespread water complaint
Found in
City water · Well water
AquaOx filters
Pair with ROAdd the AquaOx Water Softener
What it does to you
Health effects
Hard water has no documented adverse health effects. The calcium and magnesium that make water hard are essential dietary minerals, and several long-term population studies suggest a small protective effect against cardiovascular disease in regions with naturally hard water.
What hard water does cause is a long list of cosmetic and household problems: white scale crusting on shower heads and faucets, soap scum that will not rinse off skin or tile, dry itchy skin after showering, dull or straw-feeling hair, water spots on dishes and glassware, reduced lather from soap and shampoo, and significantly shortened life on water heaters, dishwashers, washing machines, and coffee makers.
None of this is dangerous. All of it is annoying. The combined cost in extra detergent, shortened appliance life, and plumbing repair is what drives most people to install a softener.
Where it comes from
How it gets into your water
Calcium and magnesium dissolve into groundwater from limestone, chalk, and dolomite formations. Most of the United States sits on rock that contributes some hardness, with the heaviest concentrations across the Midwest and Plains where limestone aquifers dominate. Florida and Texas also see consistently very hard water from carbonate-rich bedrock.
Surface water sources tend to be softer than groundwater, but cities that draw from groundwater (Phoenix, Las Vegas, Indianapolis, Minneapolis, San Antonio) deliver moderately to very hard water to the tap. Hardness is one of the few water-quality parameters that almost never changes after treatment, since utilities rarely soften water before distribution because of the cost.
Limestone aquifers
Calcium and magnesium leach from carbonate rock
Dolomite formations
Magnesium-rich rock common across the Midwest
Unsoftened city water
Most utilities do not soften before distribution
Scale precipitation
Heat in water heaters drops calcium out as scale
Find out for yourself
Is it in your water?
Hardness is the most visible water issue in any home. White crusty deposits on shower glass, scale rings inside the toilet bowl, spots on clean dishes, and soap that refuses to lather are the textbook signs. If your skin feels dry and your hair feels dull straight out of the shower, hardness is almost certainly involved.
The water industry classifies hardness in mg/L of calcium carbonate: 0 to 60 is soft, 60 to 120 is moderate, 120 to 180 is hard, and above 180 is very hard. A $10 test strip kit measures it in seconds, and your CCR will list it if the utility reports it. Most of the country falls in the moderate-to-very-hard range.
The fix
How AquaOx filters it
The AquaOx whole-house purifier is not a softener. It filters chlorine, VOCs, disinfection byproducts, heavy metals, and most of what is on the EPA primary contaminants list, but it leaves calcium and magnesium in the water because those minerals require a fundamentally different filtration technology: cation exchange.
For hardness, we sell the **AquaOx Water Softener** as a dedicated companion system. It uses high-capacity resin to swap calcium and magnesium ions for sodium ions, delivering soft water to every fixture in the house. Most homes that have both an AquaOx purifier and an AquaOx softener install them in series: softener first, then the purifier downstream. That order protects the purifier media from scale and gives you both clean and soft water at every tap.
If you do not want softened water at the kitchen sink (some people prefer the taste of harder water for drinking and cooking), the softener can be plumbed to skip the cold kitchen line. Talk to our sales team about sizing if your hardness is above 25 grains per gallon or you have iron in addition to hardness.
From the blog
Reading on Water Hardness
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