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Hard Water

What is it?
Hardness is a measure of dissolved minerals (usually calcium and magnesium) in water. As water comes into contact with soil and rock, it dissolves naturally-occurring minerals resulting in increased hardness. Hardness is measured in milligrams of calcium carbonate (CaC03) per liter (mg/L) or in grains per gallon. As shown below, water with hardness over 180 mg/L is considered very hard. The hardness in groundwater in Santa Clara County ranges from 10 mg/L to nearly 600 mg/L, with an average of 280 mg/L. By comparison, the District’s treated surface water ranges from 30 to 280 mg/L, with an average of 105 mg/L.

Water Hardness Scale

mg/L Grains per gallon Classification  
Less than 60 Less than 3.5 Soft
60 - 120 3.5 - 7.0 Moderately Hard
120 - 180 7.0 - 10.5 Hard
Over 180 Over 10.5 Very Hard


What are the health effects?
Hard water does not pose a health risk, and there is no health-based drinking water standard. In fact, hard water may help you meet daily requirements for calcium and magnesium in your diet.

What problems are associated with hard water?
Although hardness does not affect the safety of your water, it can cause aesthetic issues. Hard water can affect the taste of your water and can be a nuisance for cleaning tasks. Hard water deposits may build up on dishes, glasses, plumbing fixtures, and wash basins, and hardness may cause poor soap and detergent performance. Hard water can also cause the build-up of scale on pipes and fixtures that can eventually lead to lower water pressure and reduced efficiency of water heaters.

How do I test for hardness?
If your water comes from a public water supply, such as a city or a water company, your water is regularly tested for hardness and many other substances. Each year, retail water providers publish a water quality report to show consumers exactly what is in the water they provide. Click here to find out where your water comes from.

If your water comes from a domestic well, you may be eligible for free basic water quality testing by the water district, including testing of water hardness. Contact the water district’s Groundwater Hotline at (408) 630-2300 for more information.

If you want to test your water for hardness, the water district recommends that you use a state-certified laboratory. Click here for a list of local certified labs.

How can I treat it in my water?
Hardness does not pose a health hazard, but if you want to reduce the hardness of your water for aesthetic reasons, you can install a water softener or ion exchange system. These systems can increase the sodium content of your water, which may pose health concerns for your household. These systems may also contribute additional salts to wastewater treatment plants and ultimately to recycled water, which is reused for other purposes. If you want to avoid the use of water softeners or ion exchange systems for health or environmental reasons, there are cleaning products and natural remedies (such as vinegar) that will help to address mineral build-up caused by hard water.