Hard water in California: why it happens and what to do

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What hard water is

"Hard" water simply has more dissolved calcium and magnesium. Hardness is usually reported as milligrams per liter (mg/L) or parts per million (ppm) "as calcium carbonate," or in grains per gallon (gpg). One grain per gallon equals about 17.1 mg/L. The U.S. Geological Survey's hardness of water page uses this scale:

• 0 to 60 mg/L: soft
• 61 to 120 mg/L: moderately hard
• 121 to 180 mg/L: hard
• More than 180 mg/L: very hard

Hardness is not a health contaminant. There is no federal or California MCL for it, and calcium and magnesium are ordinary dietary minerals. It is an aesthetic and maintenance issue, which is exactly why so many California homeowners search for it: it shows up as white crust on faucets and shower glass, spots on dishes, and scale inside water heaters, tankless units and appliances.

Why so much of Southern California has hard water

Most of urban Southern California relies heavily on imported water wholesaled by the Metropolitan Water District of Southern California (mwdh2o.com). Two major imported sources feed the region: the Colorado River, via the Colorado River Aqueduct, and Northern California water carried by the State Water Project. Colorado River water picks up minerals across a huge, dry watershed and is notably harder and saltier, while State Water Project water is generally softer. How hard your tap water is depends on how your local utility blends those imports with local groundwater, and the blend can change from year to year with drought and allocations.

Local groundwater adds its own signature. Many Inland Empire and San Diego County utilities pump from basins with moderately hard to hard water, and some coastal and desert systems are harder still. By contrast, systems that rely mainly on Sierra Nevada snowmelt, such as San Francisco's Hetch Hetchy supply or the East Bay's Mokelumne River supply, tend to be soft. Sacramento-area surface water is also generally on the soft side.

The practical takeaway: two neighbors in different water districts can have very different hardness, and the same house can see a different number after a dry year. Always check your own utility.

How to find your hardness number

1. Your Consumer Confidence Report. Most California CCRs list "Total Hardness" (and often calcium and magnesium) under general mineral or secondary constituents. Note the units; some list mg/L, some list grains per gallon, and some list both.
2. Drinking Water Watch. The State Water Board's Drinking Water Watch has each system's sampling results, including hardness for most systems.
3. A test strip at the tap. Inexpensive hardness strips give a quick reading in gpg. They are less precise than a lab but useful if you are on a private well or want to confirm a softener is working.
4. Your TapCheck ZIP report. Enter your ZIP above and confirm the utility on your bill.

What hard water does in a home

• Scale in water heaters. Calcium carbonate precipitates faster in hot water, so tank and tankless heaters collect scale. Manufacturers commonly recommend periodic flushing or descaling in hard-water areas; check your heater's manual.
• Fixtures and glass. White spots on shower doors, crusty aerators and showerheads, and film on dishes.
• Soap and detergent. Hard water reacts with soap, so it lathers less and can leave a film on skin and hair.
• Appliances. Dishwashers, coffee makers, ice makers and humidifiers all accumulate scale.

Options: softeners, scale control and filters

Ion-exchange softeners swap calcium and magnesium for sodium or potassium and are the traditional fix for whole-house hardness. In California, check local rules before installing one: state law lets local agencies restrict salt-discharging residential softeners where discharges harm recycled-water supplies, and some Southern California sanitation districts have done so. Your city or sanitation district can tell you what is allowed. Potassium-based or exchange-tank (off-site regeneration) service are common alternatives.

Salt-free "conditioners" (for example, template-assisted crystallization) do not remove hardness minerals; they aim to reduce scale formation. Look for independent test data rather than marketing claims.

Reverse osmosis at the kitchen sink removes most dissolved minerals from drinking water, but it is a point-of-use system, not a whole-house hardness fix.

Carbon filters improve chlorine taste and odor but do not soften water.

Whatever you choose, look for independent certification: NSF/ANSI 44 covers residential cation-exchange softeners, and the NSF certified products listings let you check a specific model. Our filter basics page compares the main system types.

Hard water by region

See how your area's supply is described on the regional pages: Inland Empire, Los Angeles, San Diego and the Bay Area, or jump to a city such as Riverside, Fontana, San Diego or Los Angeles.

Related guides

• PFAS in California drinking water
• Chromium 6 in California water
• How to check tap water by ZIP
• City water guides
• Regional water guides

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