Does Sonoma County have hard water? And do you need a water softener?

By The Downspout · Posted Oct 27, 2026 · 12 min read

Yes, moderately. Most city taps here get Russian River water with about 6.4 grains per gallon of hardness. That is enough to leave spots on glasses, but not enough to build much crust in pipes and water heaters. Hard water is not a health risk. Some city wells and private wells run harder. On city water, we would skip the salt softener.

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Six big wells stand beside the Russian River near Wohler Bridge and Mirabel Park. River water seeps down through the gravel to reach them.^[1] From there it flows to more than 600,000 people, in Santa Rosa, Windsor, Rohnert Park, Cotati, Petaluma, Sonoma and beyond.^[2]

It carries some calcium and magnesium, the two minerals that make water "hard."^[3] You meet them as white spots on your glasses and a crust inside the kettle. The real question is whether they are worth a softener: a tank of salt that costs money, adds sodium to your water and sends salt down the drain. For most homes on city water here, our answer is no. Here is why, and when the answer changes.

Our picks

Our take, before the details:

On city water that is mostly river water, skip the softener. The river supply averages about 6.4 grains per gallon (the unit is explained below). Below 7, Penn State's water experts say hard water probably won't leave much crust, called scale, or soap film.^[4] Petaluma suggests vinegar for fixtures.^[5]
On harder city water or a private well, find your number first. Over about 10.5 grains is "very hard." If scale in the water heater worries you, look first at a certified salt-free unit (see "Do salt-free softeners work?"). If that is not enough, get an efficient softener and set it up as in "If you do buy a softener."
Low-salt diet, septic system or graywater garden? Read "Sodium in your glass," "On a septic system" and "In the garden" before you buy.

How hard is your tap water?

Your water report lists hardness in parts per million (ppm), the same as milligrams per liter. To get grains per gallon, divide by 17.1.^[2] We use grains here, because a softener is set to your water's hardness in grains.^[2]^[3]

Find your number. It is in your utility's yearly water quality report, under "hardness." Our guide to reading a water quality report shows where. On a private well, only a lab test will tell you. See testing your well water.

Look at the blue bars: the river water most cities buy is moderately hard. The gray bars are cities' own wells, and most run harder.

Sources: each utility's yearly report.^[6]^[7]^[8]^[9]^[10]^[5]^[11] Data.

Your tap gets a mix. Santa Rosa's water is 95 percent river water, and its yearly average comes to about 6.5 grains.^[6] Cities that lean on their own wells run harder. Petaluma's wells averaged about 10 grains in 2025, and its well samples ranged from about 4 to 19 grains.^[5]

What hard water does, and what it doesn't

It is not a health risk. Santa Rosa says hard water is not known to cause any adverse health effect.^[2] Calcium and magnesium are nutrients your body needs.^[4] Petaluma calls hardness a quality issue, not a safety concern.^[5]
It leaves scale when heated. The white or gray crust builds up in kettles, pots and water heaters, and can shorten a water heater's life.^[4]
It makes soap work harder. Hard water leaves soap film in tubs and curds in the washer.^[4]
A softener is not a filter. It will not necessarily remove more serious contaminants.^[4] For that, see our guide to water filters for Sonoma County homes.

How a salt softener works

A softener is a tank of small resin beads coated with sodium. Hard water flows through, and the beads swap their sodium for the calcium and magnesium.^[4]^[12]

When the beads fill up, the softener recharges them by rinsing them with brine, a strong salt water from a second tank. The rinse, carrying the salt and the hardness, goes down the drain.^[4]

Each rinse uses about 20 to 70 gallons of water.^[13] Timer models rinse on a schedule whether the beads need it or not, which wastes salt and water. Demand models rinse only after a set amount of water has gone through.^[4] Choose a demand model.

What a softener costs you

Salt and water

Say your home uses about 3,700 gallons a month in winter, when little goes on the yard. That is typical in Petaluma.^[14] Run it all through a softener on river water, and it would use about 70 pounds of salt a year: almost two 40 pound bags. On water as hard as Petaluma's wells, about 110 pounds.

That assumes the least efficient softener state rules allow on a sewer: 1 pound of salt for every 4,000 grains of hardness it removes.^[15]

The rinses add water too: up to 10,000 gallons a year.^[16]

Sodium in your glass

Softening adds about 8 milligrams of sodium per liter for every grain it removes.^[12]^[17] For river water, that takes sodium from about 8 milligrams a liter to about 60.^[6]

For most people that is small: two liters a day of softened river water is about 120 milligrams of sodium, 8 percent of a 1,500 milligram daily budget, the one Santa Rosa uses.^[2] For someone limited to 500 milligrams a day, it is three times EPA's guidance of 20 milligrams per liter of water.^[18]

On a sodium-restricted diet? Ask your doctor before softening.^[17] Keep one cold kitchen tap off the softener for drinking and cooking.^[17]
Potassium chloride can replace salt in most softeners. It costs more, and you use about 10 percent more of it.^[12] People with kidney disease should ask a doctor first, since extra potassium can be a risk for them.^[19]

Money

The hardware alone runs about $500 to $1,500, before installation, salt and upkeep.^[4]

Where does the salt go?

Down the drain, and it doesn't disappear. Chloride, half of salt, does not break down,^[20] and ordinary sewer treatment does not remove it.^[21]

That matters here because much of our wastewater gets a second life. Santa Rosa's Laguna Treatment Plant cleans wastewater from more than 225,000 people in Santa Rosa, Rohnert Park, Cotati and Sebastopol. Its recycled water is used to irrigate farms, vineyards, parks and playgrounds.^[22] More in our guide to where your wastewater goes.

Saltier water in, saltier water out. North Coast water quality regulators list water softeners among the salt sources that make wastewater saltier than the water that came in. Discharges from treatment plants and septic systems can raise salt levels in groundwater.^[23]
Reuse gets harder. A research project led at Arizona State University and funded in part by California's State Water Board starts from the point that home softeners can become a major source of dissolved salt in city wastewater, which limits how that water can be reused.^[24]
Fresh water turns salty. EPA researchers name water softening as one cause of rising salt in rivers and lakes worldwide.^[25] At high, steady levels, chloride, the other half of salt, can hurt fish and other water life and burn crop leaves.^[21]

In fairness, softeners are one salt source among several. Tap water and laundry products carry salt too, and in Santa Clarita, removing softeners cut the salt in wastewater a lot but not enough on its own.^[21] Our view: the salt you never buy is the one that never reaches the river, the fields or the fish.

On a septic system

On septic, the brine and the extra rinse water go into your tank and drainfield, the buried pipes that spread wastewater into the soil.

The case for caution. EPA says softener discharge can affect septic systems, and advises asking your septic maker or a local septic service first.^[13] A 2007 commentary by a trainer at a septic equipment maker says most makers of advanced treatment units (septic systems with extra treatment equipment) void the warranty if brine goes in.^[26]

The case it is fine. The softener industry's trade group says efficient softeners do no harm to septic systems and may even help. Very inefficient ones could cause trouble.^[27]

Our take: ask Permit Sonoma, the county permit office, before you add a softener on septic.^[28] If your septic has a treatment unit, ask its maker too. On any septic, choose a demand model so less brine goes in. Our septic guide covers the basics.

In the garden

Keep softened water off your plants. Its sodium can harm plants and soil.^[17]^[29] Sodium makes soil crust over and lets water soak in more slowly.^[30]

Graywater users: if you send laundry water or shower water to the garden, keep those lines off the softener.^[29] Or switch to potassium chloride: UC Master Gardeners say the graywater it makes is not toxic to plants.^[31] It still adds chloride, the other half of salt, to the soil and the sewer.^[21]
Never send brine into the yard or a dry well. Near Santa Clarita, the local sanitation district says that is illegal.^[21] Our guide to dry wells explains what belongs in one.

Are water softeners banned in California?

No, not statewide. A softener that drains to a city sewer is legal if it meets three main rules:^[15]

It rinses on demand, not on a timer.
It is efficient: certified to remove at least 4,000 grains of hardness per pound of salt, for units installed since 2002.
Outdoor faucets get unsoftened water, where the plumbing allows.

Those rules cover softeners that drain to a sewer or are recharged off site. They do not spell out softeners that drain to a septic system.^[15] On septic, ask Permit Sonoma before you install one.

A city or sewer district can limit or ban new softeners, but only by ordinance, and only after an independent study of its salt shows a ban is needed to meet its state permit. Softeners already in place can stay.^[32]

A 2009 state law lets sewer agencies in some regions go further, even forcing old softeners out. Sonoma County is not one of those regions.^[33]

The best-known ban is Santa Clarita's. Voters there required automatic softeners to be removed by June 30, 2009. That cut the salt in the area's wastewater a lot and saved over $70 million in treatment costs, but it was not enough alone. The district still built a plant to take salt out.^[21]

Before you buy, call your city's sewer or utilities department and ask whether it has softener rules.

One option sits outside these rules: exchange-tank service, where a company swaps your softening tank and recharges it at its own plant, so no brine goes down your drain.^[15]^[33]

Do salt-free softeners work?

Most salt-free units don't remove hardness. They change it so it is less likely to stick as scale.^[34]

Crystallization units use special beads to turn hardness into tiny crystals that don't stick.^[34] In lab tests for that same Arizona State study, they cut scale by more than 88 percent.^[24]
Electronic and electromagnetic units cut scale by about half in that test.^[24] Still, University of Nebraska experts call magnetic and electromagnetic devices unproven: scientists have not agreed that they work.^[34]
Results vary from home to home, so check a product's claims before you buy.^[34] A salt softener is the option that actually removes hardness, and it cut scale well in the same tests.^[24]^[34]

EPA suggests a unit certified for scale reduction: look for IAPMO/ANSI Z601 on the label.^[13]

Our take: if scale in a water heater is your main worry, look at a certified crystallization unit before a salt softener. It adds no sodium and no brine.

If you do buy a softener

Get an independent lab test first. Free tests from sellers can lead to buying more than you need.^[4]
Choose a demand model with high salt efficiency. Skip timer models.^[13]^[15]
Soften only what needs it. Leave toilets and outdoor faucets off the softener,^[4]^[15] and keep one cold kitchen tap unsoftened for drinking.^[17]
Set it to your water's hardness, from your report or lab test.^[2]
Hire a licensed plumber. See finding a water pro.

What it means for you

Look up your number in your utility's water quality report or a well test.
Under 7 grains: vinegar, not salt.
Over 10.5 and scale is a real problem: a certified salt-free unit or an efficient demand softener, set up as above.
Either way, keep softened water out of the garden and out of graywater.

Next: where your tap water comes from and how it is treated, in our tap water guide.

Photos by Devan Hemmings unless noted.

Sources

Checked 2026-10-27. Rules and programs change. If something here is out of date, the source above wins. Spot an error? See our corrections policy.