Hard Water vs Soft Water: The Difference, How to Tell Which You Have, and When It Is Worth Fixing

People ask me, "What's the difference between hard water and soft water?" Usually the question behind it is one of three: do I have hard water, is it doing anything to my house, and is it worth fixing. This page is the answer I give on the phone: what the two words actually mean, how to tell which one you have before you spend a dollar on a test, what hard water does to pipes, appliances, skin and hair, whether softened water is safe to drink, the hardness number where a softener is worth installing, how a softener works, and why soft water feels slippery the first week.

Under two minutes on camera: the difference, the lather test, what scale does to a pipe, whether soft water is safe, the 7 grain line, how a softener works, and why soft water feels slippery.

What hard water is, and what soft water is

The calcium and magnesium in hard water come out of the rock the water passed through on its way to your well or your utility's intake. Here is how I explain it on the phone: rainwater seeps through the soil and rock, and where that rock is limestone or another soft rock, the water eats it up and comes out hard and neutral. Where the rock has nothing to dissolve, the water stays soft, and usually stays acidic too. That is why a well one town over can test completely differently from yours, and why a house on city water gets whatever hardness the utility's source has.

Hardness is measured in grains per gallon (gpg). If a report gives it in mg/L or ppm instead, divide by 17.1 to get grains. The chart shows the four U.S. Geological Survey bands.

Hard water is common. Of the 343 certified lab reports from the water test kits people have bought through us, the median hardness was 5.7 grains per gallon, 42 percent came back at 7 gpg or above, and 30 percent were over 10.5 gpg, which the USGS calls very hard. About a third were genuinely soft.

How to tell which one you have

The quickest check is in the shower: with soft water you get tons of foamy bubbles when you wash your hair or lather up; with hard water the soap barely foams and leaves a film. That is the test I give people who do not have a fancy test. Hard water reacts with soap to form soap scum, which is why you need more soap, more shampoo and more detergent to get anything clean, and why the ring forms in the tub.

The house shows the rest. A homeowner in Nevada called us because his water "makes these white spots" on all of the dishes; another caller in Texas described "a lot of scale" everywhere the water touched. Here is what each sign means:

Signs tell you that you have hard water. They do not tell you the number. If all you want is a yes or no, a $20 strip kit from the hardware store is enough, and how to test water for hardness walks through it. The certified test below is for the step after that: if the strip says hard and you are going to buy a softener, the softener is sized to your exact grains per gallon, and a strip cannot give you that. On a private well that has never been tested, the full well water test covers hardness, iron, pH and bacteria in one report instead.

Certified lab test, $99

Buying a softener? Get the exact number first

One certified lab test, mailed to you and run by an accredited lab, reports your hardness in grains per gallon. That is the number a softener is sized to.

Get the certified hardness test

Works for city or well water. Results reviewed by Aidan, in plain English.

What hard water does to a house

Hard water is not a health problem; the damage is to the house: it builds up in the plumbing and every water-using appliance until, over time, it closes off the pipe. We have seen installations where we cut the pipe out and you could barely get a pencil through the hole in the calcium buildup. That is the end stage of scale, and it starts the day the water enters the house.

The water heater takes the worst of it. Calcium carbonate drops out of hard water fastest when the water is heated, so the heater's tank and element scale up first. The USGS lists the results: shorter equipment life, higher heating costs, lower efficiency in electric heaters, and clogged pipes. Dishwashers, washing machines, coffee makers and ice makers scale up the same way; the reason people run vinegar through a coffee pot is to dissolve that scale. On the plumbing side, scale narrows the pipe from the inside the same way cholesterol narrows a blood vessel, and the first thing you notice is pressure dropping at the fixtures.

On you, hard water does two things. It does not let you wash the shampoo out of your hair, and it causes dry skin. Both come from the same soap film: the minerals in the water react with soap and shampoo to make a curd that sticks to skin and hair instead of rinsing off. None of that is a reason for fear, but it is a reason to put a number on it.

Is soft water safe to drink?

Yes, softened water is safe to drink. We use it for everything: all types of cooking, tea, coffee. We water all of our plants in the summertime with it, and they thrive. The USGS notes that hard water can be a small dietary source of calcium and magnesium, and the World Health Organization says the same, but most people get those minerals from food, not water.

The one real trade-off is sodium. A salt-based softener works by swapping the calcium and magnesium for sodium, and the amount it adds depends only on how hard the water was to begin with: about 7.9 mg of sodium per liter for every grain per gallon removed (Penn State Extension rounds it to 7.5 mg per quart per grain). The table shows what that means in a glass of water.

For most people that is a rounding error next to food. It does matter for someone on a doctor-ordered very low sodium diet: the EPA's drinking water advisory for people limited to 500 mg of sodium a day is 20 mg/L, and softened water at 10 gpg is past that. The fix in those houses is simple: run a hard-water line to the kitchen cold tap, or put a reverse osmosis unit under the sink for drinking water. Soft water does not remove anything else from the water either; bacteria, nitrates, arsenic and the rest need their own equipment, which is why we test before we recommend anything.

How hard is too hard? The 7 grain line

When you get to 7 grains per gallon or above, you need to install a water softener. That is the line I give every caller, and it matches the USGS scale: 7 gpg (120 mg/L) is where "moderately hard" becomes "hard." Below it, the spots and the soap film are a nuisance you can live with; at and above it, scale is forming fast enough in the water heater and the pipe to shorten their lives.

For scale: a caller in Colorado read me a lab report of 238 mg/L, and I told him that is almost 14 grains, extremely hard water, probably etching his pipes. In our lab data, 42 percent of homes were at 7 or above, so if the signs above sound like your house, the odds are you are on the fixing side of the line.

Two cases where the number is not the whole story. First, hardness between 3.5 and 7 is a judgment call: fix it if the spots and the dry skin bother you; otherwise it is not urgent. Second, if your well water is acidic and you are putting in an acid neutralizer (a tank of crushed limestone that raises the pH), know that it makes the water harder; one verified buyer watched his hardness climb to about 8.7 grains after his went in. Fix the pH first, run it two weeks, retest hardness, and add the softener only if the retest is 7 or above. Details are on the neutralizer and softener page.

Ask Aidan

Have a hardness number and not sure if it is worth fixing?

Text me the number, or a photo of the report, and how many people are in the house. I'll tell you whether you need a softener, which size, and whether anything else on the report matters.

Text Aidan 443-277-2204 Call800-460-5810Aidan

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How a water softener makes water soft

A softener is a tank filled with a special cation resin; as the water passes through, the resin acts like a magnet and pulls the hardness out, and every so often it regenerates to recharge the bed. Each resin bead carries sodium. When hard water flows through the bed, the beads grab the calcium and magnesium and let go of sodium in their place, which is the exchange that makes the water soft and is where the sodium in the table above comes from. When the beads are full, the valve on top draws salt water from the second tank through the resin, the salt knocks the calcium and magnesium off the beads, and the whole load goes down the drain. That rinse is the regeneration. On a metered valve like the Fleck 5600SXT it happens based on how much water you actually used, which in a typical house is about once a week to once every two weeks.

Programming it is three settings: the time of day, the grain capacity of the unit, and your raw water hardness. You do not change anything else, and it regenerates on its own from there. The resin itself lasts a long time; the 10 percent crosslink resin in our softeners is rated for roughly 12 to 15 years against 8 to 10 for the standard 8 percent resin most brands ship. The full mechanism, valve by valve, is on Water Softeners: The Complete Guide, and what happens during a cycle is on water softener regeneration.

Two things a softener does not do. It does not remove iron beyond a small amount: under about 2 ppm the resin can carry it, but above that the iron needs its own filter ahead of the softener, which is the subject of iron filter vs water softener. And a so-called salt-free softener does not remove hardness at all; it changes the hardness into a crystal that has a harder time sticking to the plumbing, and the water still tests hard. That is a different product for a different problem; salt-free water softeners explains where it fits.

Why soft water feels slippery

Soft water feels slippery because soap no longer leaves a curd or film on your skin, so your natural skin oils come out through the pores; the slippery, slimy feeling is your skin, not the water. People get this backwards constantly. I had a customer call the week after his install because his wife could not "wash the soap off." What she was feeling was clean skin with its own oils on it; with hard water, the soap film had been sealing the pores for years. You get used to it, to the point that when you stay in a hotel without soft water the hard water feels wrong.

The practical change is to use less of everything: a very small amount of shampoo, less body wash, less dish soap, less of every household cleaner. In the dishwasher, switch from powder to the pre-measured pods; that is what I do. Soap works the way the label intended in soft water, so the amounts you learned on hard water are two or three times too much, and the excess is what feels like it will not rinse.

One exception. If the water is not just slippery but truly slimy, and you also have an acid neutralizer, check the pH: a Virginia homeowner whose refilled neutralizer pushed his water to pH 8.6 called it "really, really slippery." Softeners do not do that; a pH climbing toward 9 does, and the fix was in the neutralizer, not the softener. If your softened water tastes salty rather than feeling slippery, that has its own page: why softened water tastes salty.

What it takes to fix hard water, and what it costs

A softener is sized to two numbers: your hardness in grains per gallon and the number of people in the house. Sizing is the whole game. A softener too small for the water regenerates constantly and burns salt. A homeowner outside Chicago with four people on a well I would guess at 10 to 15 grains was sure his old softener was broken; it was a small unit set for water that hard, regenerating all the time. A softener sized right regenerates every week or two and you forget it is there. The sizes below are the single-tank Fleck 5600SXT softeners we sell, with the household and hardness range each product page gives; prices are today's, shipped, with the resin already loaded in the tank.

When a caller lands between two sizes, I tell them to go up one; more resin means the tank regenerates less often and uses less salt for the same water, and going up a size does not hurt anything. The Chicago caller went to the 64,000. Iron pushes the size up too, since each 1 ppm of iron counts like 5 grains of hardness on the resin. The formula and a calculator are on what size water softener do I need, and the ongoing costs (salt, water used in regeneration, resin life) are on water softener cost. If you want the models compared head to head, that is the best water softener page, and every size is on the water softener collection.

Installing it is a job most homeowners do themselves. The resin ships already in the tank and the bypass valve is already on the control valve, which one buyer noted removes two install steps; another wrote that he needed two one-inch threaded PVC adapters for his lines, installed it quickly, and watched a video to go through the settings. We text you that programming video when the unit ships. The step-by-step is on how to install a water softener.

Frequently Asked Questions