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Does anyone know of any empirical studies or well-tested scientific theories on the benefits (or lack thereof) of using a home water softener?

I have a water softener in my house that we installed when we first built the place years ago. I have always been a bit skeptical, but I've heard and read claims about how soft water is "better" for your water pipes, your skin (bathing with it), your health (drinking it), etc.

Every once in a while I search the net, but I rarely see discussion of water softeners pros or cons. Those that I do fine are usually unscientific.

Some points anecdotes that add to my skepticism:

  • I personally dislike washing with soft water -- it makes it very hard to get soap off.
  • I also have a completely separate reverse-osmosis water filter for drinking water that definitely improves the taste -- but I would expect this to function independent of the softness of the input water.
  • There is often a build-up of particulate that appears to be salts/potassium from the soft water on surfaces such as the shower, the pan of swamp coolers, etc.
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    Hard water contains calcium or magnesium, which if anything is good for you. strange claims. But the calcium can build up in pipes and you need to decalcify coffee machines etc. But that's a matter of wear and cost, not health. Hey, people pay money to buy mineral water. :-) I would want links to these claims, to be honest.
    – Lennart Regebro
    Apr 15, 2011 at 17:25
  • Mostly the claims come from people selling water softeners. For example Culligan.
    – wjl
    Apr 15, 2011 at 17:48
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    Well, the claims for the "health" of the pipes and water system are valid. I recently had to replace a water heater that had so much build up that it wouldn't function, and it was no where near its useful life. Also, many areas that come in contact with water have ugly stains and other build ups. I can only imagine the condition of my pipes. Health claims are sketchy at best. I suppose if there were things that a water softener got rid of that were harmful (sulfur?), then I can see it, but other than that, I would say marketing. Oh, you would use less soap with soft water.
    – JasonR
    Apr 15, 2011 at 17:59
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    @cjk: The Culligan site doesn't actually say anywhere that the water gets healthier because it's softer. They claim that the water tastes better if you install their water treatment systems, which also includes filtering, and it can therefore very much be true. They also claim it's healthier than sodas, which also is true. But nowhere do they claim soft water is healthier than hard water.
    – Lennart Regebro
    Apr 15, 2011 at 18:29
  • The Culligan site was just an example, and is surprisingly tame in their claims. All sorts of other claims about soft water are common "in the wild". Maybe not everyone has heard them -- maybe it's a regional thing. Anyway, the details of what unsubstantiated claims isn't really that important; everything in my question beyond the first sentence with a question mark was just meant to give background -- it isn't vital to the question I'm asking. I'm looking for "empirical studies or well-tested scientific theories (or lack thereof)". Perhaps "the lack thereof" is what you all are pointing out.
    – wjl
    Apr 15, 2011 at 18:45

4 Answers 4

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There are two types of precipitate that come out of hard water: those that form "scale" and those that form "sediment." Scale will cling all over stuff. Physical removal is almost always impossible, and you typically have to use chemicals to remove it. Sediment, on the other hand, is more loose, and if you were able to stick your hand in the water heater, you could scoop it out as if it were sand. You're supposed to drain the sediment out, but most homeowners don't, and even if you do, it's only marginally effective.

  • Is soft water better for your pipes? Yes, definitely. ( lots of good info: http://www.cambridgema.gov/...pdf ; also, http://www.cdc.gov/...htm , states "often leaves a deposit on the inside of the pipe")
  • Will scale buildup reduce flow? Yes.
  • Will it completely clog your pipes? Probably not.
  • Will scale & sediment form a thermal barrier between the water and a natural gas / propane burner, or any devices intended to create or exchange heat (search for "scale" in the pdf -- second paragraph, page 14), reducing efficiency significantly? Yes.
  • Can sediment bury the lower element in an electric tank, causing it to overheat and fail? Yes.
  • Can scale pretty much destroy a tankless water heater's efficiency? Definitely. Even the tankless water heater manufacturers admit this and openly state that their systems should not be installed in hard water areas without a water softener.
  • Can scale buildup cover your temperature & pressure relief valve, interfering with its operation and rendering it useless, making it possible for a malfunctioning water heater to experience a BLEVE that would pretty much completely destroy your house? Yes.

All of this is well-known to any plumber. It's not hype by companies that sell water softeners. If I'm bored tomorrow, I'll dig up more links, but you could say that I'm involved in the heat-exchanger business, and anyone that is remotely legit is very familiar with problems posed by scale and sediment.

Is soft water better for your skin? In the sense that it won't leave soap on your skin, yes.

Is soft water better for your health? Mixed reviews. I don't think it makes much difference either way.

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    Mixed reviews? Could you elaborate on that in your answer? My environmental chemistry teacher told us that the calcium in the water was actually good for us, but we control water hardness because of the bad taste and because it blocks pipes. If it's not that clear cut, I'd love to know why.
    – Borror0
    Apr 16, 2011 at 17:32
  • Yep, but how many people drink unfiltered water from their tap? Most get it out of their fridge, which will filter out almost all of the calcium, iron, etc. On top of that, hard water will leave soap on the skin, causing irritation and pH problems, which can cause people to scratch their skin more, leading to infection.
    – Michael
    Apr 16, 2011 at 20:20
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    My point is that this should be explained in the answer. :)
    – Borror0
    Apr 16, 2011 at 21:12
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    [I drink unfiltered water from the tap.] How does a fridge filter calcium and iron? (Are you talking about filling a bottle from the tap and chilling it in the fridge?)
    – Oddthinking ♦
    May 27, 2011 at 12:29
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Well, there is hard science behind the fact that water comes in various degrees of hardness/softness depending on how much Calcium and Magnesium are in the water.

In the same way that Dripstone caves form, hard water can (and will) leave deposits of calcium and magnesium compounds in your appliances (Limescale). From that article:

Calcium bicarbonate is soluble in water, however at temperatures above 70 °C (158 °F) the soluble bicarbonate is converted to poorly-soluble carbonate, leading to deposits in places where water is heated.1 Local boiling “hot spots” can also occur when water is heated, resulting in the concentration and deposition of salts from the water.

Calcium cations from hard water can also combine with soap, which would normally dissolve in soft water. This combination often forms scum which precipitates out in a thin film on the interior surfaces of baths, sinks, and drainage pipes. Soap usually contains salts of anions from neutralized fatty acids or similar chemical compounds. The calcium salts of these anions are less soluble in water.

So up to now, everything is all nice and scientific. Next: Water softeners. There is a chemical process that will replace the calcium and magnesium ions in your water with sodium ions. The resulting compounds are much more soluble in water and do not form the unsoluble compounds, so no limescale will form. Again, this is hard science: You let the water pass through a filtering system that contains certain molecules with sodium attached, whose chemical properties allow the sodium ions to be easily replaced by the calcium and/or magnesium ions. After a while, the filter becomes saturated with the Ca and Mg ions and has to be regenerated; again, there are chemical processes that will accomplish this.

Next: The effects. It will prevent your pipes and appliances from being clogged by limescale. But what about drinking the softened water? Hard water is not unhealthy, and softened water is not healthier. In fact, since it contains more sodium than normal water, you should be careful if you have to follow a salt-restricted diet. Also, calcium is important for bone stability. For this reason, many people opt to have one tap bypassing the water softener.

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  • Hallo Baer, a lot depends on where You live. We (Germany) are used to tap water one can and does drink. On some Canary Islands water is from desalination and very soft, which makes it corrosive to copper often. Today soaps are "hardness-proof", for that reasons I would say, water-softeners are very good for the wallet of the seller.
    – No longer here
    Apr 16, 2011 at 11:47
  • It is better for your appliances, though: No encrusted shower heads and clogged coffee makers.
    – Lagerbaer
    Apr 16, 2011 at 14:08
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(Disclosure: I work for Harvey Water Softeners in the UK)

A recent paper published by the UK Water Trade Association gives a good overview of the evidence. We've linked to it from our site:

A particularly strong source is a study by the Battelle group in the US. That's another one we've highlighted on the site:

Of course, we're fairly positive about the studies in the blog posts I'm linking to, but they link to the original documents so you can check them out for yourself.

The more lifestyle-related benefits, such as softer skin and eczema relief are well-supported anecdotally, but less well in terms of hard science.

The most well-supported benefits are related to limescale removal: energy savings, reductions in washing powder/detergent, and longer-lived appliances.

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In the UK there was a randomised controlled trial to see if water softeners improve eczema symptoms in children. The conclusion was that it didn't:

The average eczema score reduction in the water softener group was 20% (5 points improvement on SASSAD) compared with a 22% reduction in the control group (5.7 points improvement on SASSAD). We also compared the number of children who responded particularly well during the trial (i.e. those who had a good or excellent response), but again there was no difference between the water softener group and the normal care group.

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