Tiny Water Treatment
water treatment for small spaces


Water Softeners

Ever since Emmett Culligan popularized in-home water treatment in the 1930s, water softeners have been big business.  And for good reason—treated water offers real, tangible benefits to homeowners.

Hard water has a high concentration of the minerals calcium and magnesium.  Various tests can determine hardness concentration, which is generally expressed in parts per million (PPM or mg/L), or grains per gallon (GPG).  Grains per gallon (1 GPG = 17.1 PPM) is an imperial measurement that is popular in the water treatment industry.

Hardness can be measured with drop tests for Total Hardness or Calcium Hardness.  But the original water test for hardness is still one of the simplest: the soap test.  A sample of water is mixed with liquid soap, drop by drop, and shaken.  The number of drops of soap required to maintain suds in the water correlates to the level of hardness in the water.  More soap needed means more hardness is present.

The Problem with Hard Water

Calcium and magnesium have a strange property called inverse solubility.  While most solids tend to dissolve better in hot water than cold (e.g. sugar, table salt), calcium and magnesium tend to dissolve better in cold water than hot.  As a result, as water is heated, the amount of hardness it can keep in solution drops, and hardness precipitates as a solid rock called lime scale.  The hottest part of the plumbing system tends to be the worst possible place for hardness scale to accumulate -- water heaters and hot water appliances.  High pH also decreases the solubility of hardness, so dishwashers and washing machines are especially susceptible to scale damage due to their alkaline detergents.

Hardness also reacts with soap to form a solid white substance called soap scum.  This makes the soap in solution unavailable washing, so you need to add far more soap to do the same job, and it causes soap scum to accumulate on your clothes, shower walls, inside your appliances, and on your skin and hair.

How Water Softeners Work

Water softeners work by ion exchange, a process by which one ion attached to a resin bead is traded for another in solution.  Physically, water softener resin is made of amber colored beads around 1/4 to 1/2 mm in diameter.  On the chemical level, the surface of the resin beads are covered in sodium ions.

Softener resin is cation exchange resin. A cation is a positively charged ion. The positive half of each mineral salt is a cation: the Na+ in NaCl, the Ca2+ in CaCO3, the Mg2+ in MgO. The negative half is the anion: Cl-, CO32-, O2-. Cation exchange resin exchanges one cation for another, in this case, sodium for hardness.

Zeolite resin beads are negatively charged, so positively charged sodium (Na+) sticks to them like a magnet. But zeolite resin would rather have a calcium (Ca2+) or a magnesium (Mg2+), so when one of those particles floats by, the resin releases a sodium so it can grab a hardness ion.

Eventually, the softener resin runs out of sodium ions to trade for hardness, and must be regenerated. A 10% solution of sodium chloride dissolved in water (brine) is used to rinse the accumulated hardness ions from the resin bed and replace them with sodium. Once the softener is regenerated, the softening process can start over.

While not a component of hardness, dissolved iron (Fe2+) and a handful of other cations can also be removed with a water softener. While particulate iron should be removed with a prefilter, softeners are helpful for removing dissolved iron that can cause sediment and staining problems downstream.

Benefits of Softening Water

Using a softener to remove hardness from your water can stop accumulation of lime scale, allow your soaps and detergents to work better with less, and prevent the formation of soap scum.  The results are appliances that last longer with less maintenance, softer clothes, spot-free dishes, a cleaner shower, and softer skin and hair.

When you shower with soft water, you'll notice a difference in the feel of the water.  Soap feels more slippery and produces suds much more freely.  Many people complain at first that the soap won't wash off with soft water because their skin feels slippery.  In fact, that's what your skin is supposed to feel like when it's not covered in a layer of soap scum.  Just get out of the shower and dry off, and enjoy the feeling of cleaner skin.

You'll need to use far less soap when using soft water.  People with long hair who used to need a handful of shampoo to wash their hair will need closer to a quarter sized bit of shampoo.  You'll also want to use far less detergent in your washing machine and dishwasher, and you can check the machine's manual for instructions on using it with soft water.

Disadvantages and Limitations of Water Softening

Softeners do their job well, but they don't do everything. 

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A softener is not a purifier.  Softener are trading hardness ions for sodium ions, so for everything they remove, they're adding back an equivalent amount of sodium.  If you're on a sodium restricted diet, the amount of sodium added in your water can be significant.  If that's the case, it's best to also use a drinking water system that removes the sodium, so that you have room for some salt in other parts of your diet.

A softener does not remove pathogens from your water.  In fact, the resin can provide microorganisms lots of surface area to grow.  In most cases, you want the water you're feeding the softener with to already be microbiologically safe.

A softener is not a great sediment filter.  If your water contains sediment, you'll want to filter it out before it hits the water softener.  While softeners do have backwash cycles to remove accumulated sediment, lots of sediment can still clog up the tank and cause maintenance problems.  If the sediment is heavier than the softener resin (e.g. sand), the backwash cycle will not be strong enough to remove it, and it will accumulate in the softener until the softener breaks.  For mobile setups, I recommend a 10" standard Pentek housing with a 5 micron filter element, a wrench, and a mounting bracket.  For a sticks and bricks house, I recommend using a 20" Big Blue filter with a dual density 25/01 micron filter element—change it annually or sooner if you notice a pressure drop.  Don't forget the mounting bracket and wrench.  If you're a professional, get this wrench for the Big Blue instead.  In fact, get two.  It's surprisingly difficult to open a filter housing that a homeowner over-tightened when they last changed the filter.

If you're using a softener to remove iron, you're going to want to regenerate it with an iron removing additive like Iron Out powder in addition to your salt.  Iron Out is a reducing agent that converts insoluble red iron to soluble clear iron that can be washed away.  It's also great for getting rust stains out of fixtures and clothes, or restoring rusty tools.  Bagged water softener salt is also available with the Iron Out additive already applied to the salt, which can be useful if you are using an automatic water softener to remove rust.  Don't mix Iron Out with any other water softener cleaning chemicals, or with bleach.

Softeners are susceptible to damage from chlorine.  If you're installing a water softener long-term on a chlorinated water supply, it's sometimes a good idea to put a carbon filter ahead of it to protect the resin.  For mobile setups, I need the chlorine for my tanks, so I leave the chlorine in.  I just understand that my softener resin will eventually turn to mush and need to be replaced.  For a sticks and bricks house, this carbon block cartridge is a good choice, and it fits the same 20" big blue housing mentioned above.  If you have high sediment in your water as well, you're going to want to put a Big Blue sediment filter prior to the carbon block to keep it from clogging quickly.

Softeners use a significant amount of water for regeneration.  You wouldn't want to put an automatic softener on an off-grid application with a limited water supply, though a portable RV softener is usually manageable for those applications.

Softeners also discharge a significant amount of salts when regenerating, both NaCl and whatever mineral salts it has accumulated.  Continually regenerating a softener onto the same spot on the surface of the ground over a long period of time will cause salts to accumulate and kill most plants in the area.  Discharging into a drainage ditch feeding a creek or stream could also cause environmental damage to that body of water.  Local regulations vary, but generally softener discharge should go into a septic system, french drain or dry well, or public sewer.  Some alternative septic system manufacturers advise against discharging a softener into the septic, so if you have an alternative system, you may want to find an alternate place to discharge.  For mobile applications, the salt in a single regeneration—diluted with the water used for regenerating and backwash—is probably not enough to do any damage if allowed to percolate into the ground.  Avoid discharging into gardens or bodies of water.  If you're queasy about the environmental implications of discharging a little salt on to the ground, remember that there's a good chance your state government dumps truckloads of taxpayer funded salt on the streets every Winter.

Water Testing for Hardness

The soap test method or test strips are good "go/no go" measures of water hardness.  These options are inexpensive tests that homeowners can use to determine if their softener is working, or if they should consider a softener in the first place.  Similar inexpensive iron kits are also available for casual use.

Test strips are also usually sufficient for a mobile setup, since you should be softening all of your water regardless of the source.  You don't really need an accurate reading of concentration, you just need to know whether or not your softener needs to be regenerated.

For a sticks-and-bricks house, or any home with an unlimited source of water using a more traditional mechanical softener, a more precise reading is helpful.  Reliably sizing and calibrating an automatic water softener requires both a good hardness drop test, as well as good iron test.  If you're serious about water testing and you want the exact kit that I used for years of professional water treatment equipment sales and service, you can purchase an inexpensive TDS tester, this hardness, pH, chlorine, and iron kit, and a copper kit.  Go open an account at the local plumbing supply house and you'll be all set to start your own water treatment business.

To test your water, you'll want to flush the water from the faucet for a minute or so to get a good sample, then run your tests according to the instructions in your kit.

Sizing a Softener

For most off-grid and full-time RV use, this portable water softener is a good size.  It's compact and fairly lightweight.  You can minimize its weight and protect it from freezing by blowing the water out of it using a blowout plug and a portable compressor.  Regeneration frequency will depend on source water hardness and how much water you run through it, but it's easy to monitor with the included test strips.

If you're calibrating a mechanical softener and need a precise reading, you should use a hardness drop test and an iron test.  Iron uses up a lot of softener capacity, and it's the first thing to break through the softener when capacity is running out.  Add 4 grains for each PPM of iron to your total hardness reading (in GPG) to get your effective hardness.  For instance, if you read 10 grains of hardness and 1 PPM of iron, your effective hardness will be 14 grains per gallon.

Each cubic foot of softener resin has about 30,000 grains of capacity (more or less depending on salt dosage).  For a 1 cubic foot softener, divide 30,000 by your effective hardness in the previous step, and you know how many gallons your softener can treat between regeneration cycles.  If your effective hardness is 14 GPG, 30,000 / 14 = 2,143 gallons.  I like to keep 10% capacity as a buffer, so I'd probably set the softener for 1,950 gallons between regenerations.

If the average person uses 100 gallons of water per day, in the above example, a family of four would use up the softener capacity in less than 5 days.  If the softener is a timeclock unit, I'd set it to regenerate every 4 days, or twice a week.  If it's a digital water meter unit, I'd just set it to regenerate ever 1,950 gallons and let it figure out when to regenerate. 

It's best to keep a household softener from having to regenerate more than once or twice a week, so depending on the family size and water chemistry, you might use a larger unit that contains 1.5 or 2 cubic feet of resin.  For these units, multiply 30,000 grains by the number of cubic feet of resin used in the first step, then proceed with the calculation as before.

Choosing a Softener Model

Companies in the water treatment field have four main ways to distinguish themselves among their competitors.

Bells and Whistles

Softener resin is an old technology, and everyone has it.  The difference between technology comes down to the mechanical parts of the softener.  Timers, meters, probes, programming, reporting, remote monitoring, and other bells and whistles can add to your softener's efficiency and usability.  But at the end of the day, soft water is soft water.  A manually regenerated dumb tank full of water softener resin will produce the same soft water as the super premium high-tech automatic softener.


Most big name water treatment devices, as well as the "generic" devices sold by local plumbing shops (valves manufactured by Clack, Fleck, and Autotrol) are designed to be serviceable, and repair parts are readily available.  Cheap hardware store models with rotary valves, while theoretically possible to work on, are a nightmare to service.  And since they're so cheap, hardware store models are usually best replaced when they break.

Customer Service 

If you're purchasing from a company that is performing water testing, equipment specification, installation, and service work for you, those services have value that will add to the price of your water treatment system.  While a one-size-fits-all approach can work well for nomads, someone with their own water source might benefit from a custom approach.  An experienced water treater may be able to tailor a better system to fit your needs, address more difficult water treatment problems, or just give you a turnkey system so that you don't have to worry about installation or maintenance yourself.


Big name water treatment companies tend to be more expensive due to marketing budgets and cutting edge bells and whistles.  Local plumbing companies can often design treatment approaches that work just as well, but beware fly-by-night outfits that disappear once the product is installed.  Availability for future service and maintenance work has value.  Of course, if you know what you're doing, you can buy all the same treatment technologies for a lot cheaper online or at the local plumbing supply house.  That approach works well if you want to design, install, and maintain your own system, and you don't mind taking some time to educate yourself and test your water.

If your water quality is unknown or varied, as is the case for many nomadic and tiny living families, it's important to have a fairly comprehensive water treatment plan.  The good news is that it doesn't cost a lot of money or require a lot of bulky equipment to cover all of your bases.  Check out our suggestions for your lifestyle on our welcome page to get you started.

If you'd like to learn more about water treatment, especially as it relates to small space and nomadic living, stay tuned to this space for some deep dives into specific products, water problems, and strategies for water management in small spaces.  If you have a topic you'd like to hear more about, you can reach me here.

Dan Greatley