Apple #422: How Water Softeners Work

I know, upon your return from your Thanksgiving break, the first thing you wanted to know about is . . . water softeners. You've been burning with curiosity, even waking up in the middle of the night asking yourself, how do those dang things work?

Well, maybe you haven't. But my friend Bob who just had surgery asked me to find out about them. He didn't want me to find out about gall bladders or surgical implements or nurse's scrubs. No. What he asked me about is water softeners. So, for Bob, here's how water softeners work.

In a nutshell, water softeners take hard water and make it soft. But we must crack that nutshell and ask, what is “hard” and “soft” water?


Hard Water

Out in the great wide world, water travels over rocks and through soil. As it does that, it picks up stuff. Of the stuff it collects, what we’re concerned with here are minerals, two in particular: calcium and magnesium. Water that has lots of calcium and magnesium in it is considered hard water.

Generally speaking, hard water can make life harder. Because of the calcium and the magnesium, it’s harder to get stuff clean. Your water heater has to work harder and it might get clogged up by those minerals. The rest of your house’s plumbing could get could get clogged by those minerals, too.


This is what hard water can do to pipes and fixtures, over time.
(Photo from Tommy Dorsey Water Conditioning)


Water that’s been softened has had most or all the calcium and magnesium removed. Most municipal water suppliers soften their water at least somewhat before sending it through their water lines to your house.

But many people do still have hard water. One source estimates that 75% of homes have hard water. I’m a bit skeptical of that percentage. It might be more accurate to say that 75% of homes have some degree of hard water. Like so many things, whether or not your house has hard water may not be a simple yes/no situation.

You can tell your water is hard if

• After you wash the dishes, there are white filmy spots on them

• The glass in your shower stall is frequently coated with a white film

• Your clothes seem stiff and soapy-feeling even after you’ve washed them

• You notice a white scale or even crystals in the little filter traps over the faucets

• Instead of forming a nice, happy foam, soap tends to form a sticky, lumpy curd

One of the telltale signs of hard water
(Photo from eHow)


Here’s one layperson test you can do to get a good indication of hard water-ness:

• Find a bottle that has a cap you can close and fill it about half full of water

• Squeeze in about 10 drops of dish washing soap

• Close the cap tightly & shake.

• If the solution in the bottle makes a happy foam right away, you don’t have to worry about hard water.

• If, however, the solution doesn’t get foamy but instead makes a soapy film on the inside of the bottle or even forms a lumpy curd, you’ve probably got hard water.

If you think you have hard water, the next question is, how hard is it? To find that out, you’ll need to have someone come and do a water analysis for you. Any place that sells water softeners will be happy to analyze your water for free – because they think they’ll be able to sell you a water softener afterward. Look in the Yellow Pages under “water analysis” to find someone near you, or for a slower response, you can contact your state's certified water testing laboratory.

A professional water analysis will give you a magic number that indicates how hard your water is, or how much calcium & magnesium is in it. The magic number is usually expressed in terms of grains per gallon (GPG), or if you’re going with the British units, milligrams per liter (mg/l).

Here’s the scale, in GPG, of water hardness:

• Less than 1.0 = soft
• 1.0 – 3.5 = slightly hard
• 3.6 – 7.0 = moderately hard
• 7.1 – 10.5 = hard
• 10.6 and up = very hard

Knowing this magic GPG number is important because it will help you decide, first of all, if you need a water softener. If it's in the 7.1 and up range, you'll probably want a water softener. Below that, it's more a matter of personal preference than concern for the clogs that might build up in your pipes or water heater.

You'll also want to know this magic GPG number if you decide you do want to purchase a water softener. More on this later.


How Water Softeners Soften

Of course if you're going to get a water softener, or if you already have one, you'll want to know how they work. All water softeners have three basic parts, a mineral tank, a brine tank, and a control valve.


In this labeled photo, they're calling the mineral tank a resin tank. This photo is pretty big and I think this is an older model softener, but I wanted you to be able to see all the components.
(Photo from somewhere in the Family Handyman)


The mineral tank is hooked up to your house's water supply. Inside the tank are lots of little plastic beads. They’re made out of polystyrene and they’re called zeolites. But they’re kind of like little balls of Styrofoam. You know how those balls of Styrofoam will cling to just about anything? That’s because they have a negative charge and they’re looking for anything to fill in those missing electrons.

The hard water – which is water plus calcium and magnesium – goes into the mineral tank. The calcium and magnesium are both positively charged, so those polystyrene beads just love that calcium and magnesium. The C and Mg love them back, so much so that they will leave the water to cling to the polystyrene beads. This process is called ion exchange. But really, those minerals are so fickle.

Without the C and Mg, the water continues on, softened. Softened water feels different than hard water—slippery, almost slimy.

Softened water will also often taste salty, and that’s because of the next part of the process, the regeneration cycle.

Once enough water has passed through the mineral tank that the polystyrene beads are covered with calcium and magnesium, you either have to replace the beads or else get that calcium & magnesium off of them. It’s easier and cheaper to strip off the minerals. The main purpose of the regeneration cycle is to strip the minerals and thus make the polystyrene beads usable again.

In the first phase of the regeneration cycle, softened water is flushed back through the mineral tank to wash out any debris that might have collected in there and make the tank clean and ready to be used again. This is known as the backwash phase.


In the backwash phase, softened water is flushed through the mineral tank to wash out any nasties.
(Diagram from the Family Handyman)


The second phase – the recharge phase – starts in the second tank, the brine tank. This has a bunch of really salty water in it. Like the calcium and magnesium, sodium also has a positive charge, so the beads will like the sodium, too. The salty brine is flushed back into the mineral tank where the beads are and, though the positive charge of the sodium is weaker than that of the calcium and magnesium, the sheer volume of the sodium ions is strong enough to knock the calcium and magnesium off the beads and take their place.


During the recharge phase, salt water (brine) is flushed from the brine tank into the mineral tank to wash the calcium & magnesium off the polystyrene beads in the mineral tank.
(Diagram from the Family Handyman)


Once the beads have had time to swap partners thoroughly so that they're covered with sodium ions instead of the C and Mg, the mineral tank is flushed out and the old brine solution goes down the drain, as do the calcium & magnesium. The brine tank is then refilled so it's ready for the next regeneration cycle.

When the next batch of hard water enters the mineral tank, it will encounter those polystyrene beads that are covered with sodium ions. Since the incoming calcium & magnesium have a stronger positive charge than the sodium and since they’ll now outweigh the sodium, the calcium & magnesium will knock the sodium off and cling to the polystyrene. Thus all batches of softened water after the very first one will have sodium ions floating in it, and will taste salty.

The control valve, or timer, keeps track of this whole regeneration cycle and directs the water into the appropriate tanks at appropriate times. Depending on the type of water softener, the control valve might make the regeneration cycle happen on a regular schedule, regardless of how many of the beads are spoken for. With these types of control valves, softened water is not available during the recharging phase.

Other types of control valves are more sophisticated. They have sensors that can tell when the polystyrene beads are all full of calcium & magnesium and will begin the regeneration cycle automatically. Still others have a water meter to measure water usage and will initiate the regeneration cycle based on how much water has entered the mineral tank to begin with. These more sophisticated types of control valves will allow for a reserve of softened water so that some will be available even during recharging.


Purchasing a Water Softener

Water softeners are built to handle various levels of grain capacity (meaning grains of minerals you want to remove from the water) and water usage levels. But it's a bit confusing figuring out what size you need for your house.

Most water softeners fall in the 20,000 to 1,000,000 grain capacity range. To understand what this means for you, divide the grain capacity of the softener by the hardness of your water.

That's that magic GPG number you got when you had the water analysis done. Here's the table of grains per gallon one more time:

• Less than 1.0 = soft
• 1.0 – 3.5 = slightly hard
• 3.6 – 7.0 = moderately hard
• 7.1 – 10.5 = hard
• 10.6 and up = very hard

Let's say you can get a good price on a 40,000 grain capacity softener, and your water has a hardness level of 8. Dividing 40,000 by 8 = 5,000, which means that the 40,000 grain softener working with your hard water will produce 5,000 gallons of water per cycle.

But is that a lot or not very much? To understand what that means for your house, you also need to calculate your home's water usage.

• The average person uses about 50 gallons per day. Multiply that by the number of people in your house. This tells you the absolute minimum number of gallons per regeneration cycle you'll need your water softener to produce.

• Say you have 3 people in your house. Multiply 3 x 50 gallons per day = 150 gallons per day is the minimum amount of water your house needs.

• So a water softener that can handle 5,000 gallons in a house that only uses 150 gallons per day seems like overkill, right? Not exactly. That 5,000 gallons is how much the water softener produces before it has to run a regeneration cycle.

• Dividing the 5,000 gallons it produces by the minimum 150 gallons we need tells us that it should be 33 1/3 days before this water softener will have to go through a regeneration cycle. In other words, it would have to run a regeneration cycle about once a month. And according to what water softener salespeople say, that's about right.

• If the water softener you're considering runs on an automatic timer, which means you can't have any softened water while it's recharging, you'll probably want the softener's capacity to be larger so it doesn't have to run a regeneration cycle quite so often.

As far as how much to expect to spend, one site that's maybe a couple years old said that most water softener systems cost in the $800 to $1500 range, plus installation which is an extra $300 to $500.

After that, the ongoing costs are just electricity to run the system and monthly salt expenses which should not exceed about $2.50 per person in the household, or about $10 for an average family.


Maintenance

• Generally, you should check your water softener about once a month to make sure the brine tank has enough salt in it. The brine tank's salt level should be about half full.

• Sometimes the salt on the bottom of the tank dissolves but the top forms a kind of crust. It looks like there's enough salt in the tank but really the amount is lessening. To find out if that's the case and to break up the salt bridge if one did form, poke a blunt sort of tool like a broom handle into the salt. Be careful not to push too hard because you do not wan tto puncture the tank.

How to break up a salt bridge
(Diagram from Morton System Saver)

• If you've added more salt to the brine tank, give the softener some time before you expect it to work as it should. It will take a while for the salt to dissolve.

• You also want to make sure the brine tank is refilling with water properly. One gallon of water will dissolve 3 pounds of salt. So at least 3 gallons of water should be in the brine tank.

• Finally, you want to make sure the brine tank is clean. Gunk may build up on the floor of the brine tank, and you'll want to clean that out of there every so often.

A good water softening system can last for a decade or two without much more maintenance than this.


What Kind of Salt to Use

A lot of water softener owners want to know if it makes a difference what kind of salt they put into their brine tank.

Some water softeners are designed to work specifically with one type of salt. Read the manual to see if any products are specifically recommended and go with that. If the softener allows you to make a choice, here are your options.

Three types of salt are generally available: rock salt, solar salt, and evaporated salt.

• Of these, rock salt is the cheapest, but because it's still in the form of big crystals, it will take a lot longer to dissolve in the tank. It also contains a lot of other impurities & gunk besides salt. That gunk is going to collect at the bottom of your brine tank and you're going to have to clean that out more often.

Rock salt, in somebody's water softener brine tank. Hopefully you can see how the rock salt is crystalline.
(Photo from biodieselpictures.com)

• Solar salt was originally seawater from which the moisture was removed. It's about 85% sodium chloride (NaCl). It will have some impurities in it, but not as much as rock salt. It's usually sold as crystals so it will need some time to dissolve, but again, not as much as rock salt.

• Evaporated salt is salt mined from underground and from which the moisture is then evaporated by gas- or coal-powered plants. It's 99% sodium chloride with very few impurities. It's the most expensive of the three varieties, but it will also leave behind the least amount of gunk in the brine tank. If you use your water softener a lot and thus go through a lot of salt, evaporated salt is the recommended choice because it will require you to do the least amount of clean-out.

Solar salt and evaporated salt both get compressed into pellets like these.
(Photo from Anglian Salt)


If you're going to change the type of salt you use, wait until the salt you've been using is all gone before you switch. Mixing salts won't break your softener or do terrible damage, but using one kind at a time will keep any problems from occurring.


Should I Use Potassium Instead?

There are some problems associated with creating all that salt water. First, your drinking water will taste salty. For some people, especially those with high blood pressure, this can be quite an issue.

Here's how salty a water softener makes your drinking water:

• Initial Hardness -- Sodium Added
• 1.0 grains per gallon -- 7.5 milligrams/quart of water
• 5.0 grains per gallon -- 37.5 milligrams/quart of water
• 10.0 grains per gallon -- 75.0 milligrams/quart of water

To put this in perspective, 1 tablespoon of ketchup has 204 milligrams of sodium.

Most people solve the salty taste problem by putting a filter (Brita or some such) on their kitchen tap. But other people can't even have that much extra sodium in their diet.

Another issue with sodium is related to the brine discharge. Most places that have hard water aren't on a municipal sewer line but use septic systems. You do not want your septic tank to back up or quit working, no sir. But all the sodium in the brine discharge can screw up the bacteria count necessary to make septic systems work. This is enough of an issue that municipalities like Fillmore, CA and even entire states like Michigan, Texas, and Connecticut, have banned sodium-based water softener brine discharge.

All that sodium can also screw up the salt levels in your nearby watersheds -- rivers, marshes, what have you -- which means it makes it harder for plants to grown in that area and it changes the environment in which a lot of fishes and frogs and creatures live and breathe.

Another option besides sodium (NaCl) is potassium chloride (KCl). It's about three to four times more expensive than salt, but it won't mess with your septic tank, it won't change the fresh water surrounding your house to salt water, and it won't make your drinking water taste salty.

If you decide to make the switch from salt to potassium in your water softener, first make sure that your water softener's manual doesn't say it won't work with anything but salt. Second, make sure you've got all the salt out of the brine tank before you switch it over to potassium.



Sources
HowStuffWorks, How does a water softener work?
Thomas Klenck, How it Works: Water Softener, Popular Mechanics, August 1998
Bob Formisano, About.com, Water Hardness Testing
Galt Tech, Hard Water and Water Softeners
Bob Formisano, About.com, Water Softeners - How They Work
Lenntech Water Treatment Solutions, Water softener FAQ
Alpha Water Systems Inc, Frequently Asked Water Softener Questions
National Small Flows Clearinghouse, An Alternative to Softening with Sodium
Hamburg Township Wastewater Treatment Plant, Sodium Chloride Issues and Sodium Chloride and Water Softeners