Water Softeners: How they work

Water softeners or water conditioners (as they are frequently referred to) use a process called Ion Exchange to remove hardness minerals dissolved in water.  Some of the minerals that can be a problem in hard water are calcium, magnesium, iron and manganese. Water softeners exchange the mineral content present in the water source for sodium ions, making the water soft in the process.

Water softeners have four integral components:
1.  Control valve - Controls the water as it flows through the valve, resin bed, the distributor tube/ manifold and brine tank.
2.   Resin Tank - Holds water softening resin and gravel under-bedding.
3.   Resin - Small beads that hold the sodium “charge”.
4.   Brine Tank - Holds salt and water used to regenerate the water softening resin. 
      Single tank water softeners operate at a preset time of day usually at 2 am.  This style softener can potentially and frequently does run out of softened water when the capacity is exceeded.     

Twin Tank water softeners operate on demand. When the capacity for one tank is nearly exhausted it switches tanks and the previous tank regenerates immediately so there is no interruption of soft water. These systems use softened water to regenerate so they are very efficient with salt and water usage.

The Water Softening Process:
As hard water enters the water softener valve it is diverted to the water softener tank. Water flows down through the "resin bed" and comes in contact with the water softening resin.  The resin
beads are "charged" with sodium ions. As the hard water passes down through the resin bed calcium, magnesium and other ions (hardness) are attracted to the resin and sodium ions are exchanged. Removing the hard water minerals and delivering "softened water" to the home.

Water softening resin has a certain amount of “capacity” and has to be recharged / regenerated with sodium chloride or potassium chloride before it is completely depleted of “soft water”.  A typical residential water softener may be anywhere from 24,000 grains to 60,000 grains of capacity, generally depending on the tank size.  In basic terms the resin beads are much like a large sponge and can only attract or hold a certain amount of hard water.  The sodium is what’s used to squeeze the sponge so it can absorb again.  When a sponge becomes too saturated it gives off water.  Water softening resin has to avoid leaking off hard water so it regenerates before it becomes totally saturated with hard water minerals.  On a single tank water softener one full day of soft water is typically left in reserve for days with higher than normal water usage or times when the normal capacity may be reached first thing in the morning and the system is set to regenerate (delayed regeneration) that evening at 2 am.  This is referred to as the reserve capacity.  With a Twin Tank water softener there is no need for reserve capacity.  Nearly the full capacity of resin is used in each tank for softening. The system switches tanks (to keep supplying softened water) the other tank regenerates and goes into standby mode.  Twin tank systems also use softened water to regenerate so they are very efficient.

Water Softening Cation Exchange Resin:
The first water softening resins were natural mined zeolites.  Today most water softening resin is made of polystyrene and is manufactured for many different applications and efficiency.


Polystyrene Resin

The Regeneration Process:
When the predetermined “capacity” is reached the water softener will regenerate. Some systems may differ in their sequence of cycles. This is the most prevalent regeneration sequence used.

Regeneration Cycles:
      1.     Backwashing – Reverses the flow of water down through the distributor/manifold to clean the gravel under-bedding at the bottom of the resin tank. This lifts and loosens the resin bed and washes out oxidized particulates.
      2.  Brine Draw – A concentrated brine solution is drawn from the brine (salt) tank and washed through the resin bed displacing the hardness minerals from the resin beads, flushing them to the drain and recharging the resin beads with sodium or potassium. (This cycle may be either down-flow or up-flow through the resin tank depending on the model)
      3.      Slow Rinse – A slow rinse to rinse off excess sodium that may be present in the resin bed.
      4.      Fast Rinse – Down-flow of water to compact resin bed and prepare for service.
      5.      Brine Refill – Refills the brine (salt) tank with the proper amount of water to dissolve sodium or potassium and prepare brine solution for next regeneration cycle. (This may be the initial cycle or last cycle in some systems).
      6.      Service – Normal operating position for daily water usage.

There are five types of water softeners:
      1.      Manual - Manually regenerated by the homeowner. (Not generally in use today)
      2.      Portable Exchange - Regenerated off site by dealer and exchanged in the home.
      3.      Time Clock - Regenerates according to days a week (6-14 day timer).
      4.      Demand/Metered - Regenerates according to gallons used.
      5.      Twin-Tank Demand - Two tank system. One softener tank is in service and one in standby mode. Tanks switch during the regeneration cycle to supply conditioned water 24hrs per day, no matter the water usage.

How to Choose / Size a Water Treatment System
There are several factors important in choosing the proper water treatment system for your home.
      1.      Water analysis – Determines the total hardness (calcium, magnesium), Iron (how much, what type), PH, TDS, H2S and others.
      2.      Water Usage – Average daily water usage for your household. Most families average 75 gallons per day per person. 4 people x 75 = 300 gallons per day usage.
      3.      Fixture count / GPM – In many modern homes the Gallons Per Minute needed to operate a home are critical and needs to be part of the equation in sizing a water treatment system.
      4.      Value – Warranty, efficiency, longevity, operating cost and price.
      5.      Support / Service - The company backing the system.

Have your water tested by a reputable dealer or third party water testing lab, talk to your friends, neighbors, colleagues, check the Better Business Bureau and to search for a certified water treatment expert in your area, go to www.wqa.org.  A proper water analysis is the most important aspect of water treatment.  If you have a sales rep come to your home for a water analysis have them test the water directly from the well and through a Demo-Softener (they should all have a demo softener) to help determine the type of iron present or any other problems with the water.

Here is a general water analysis and how a water softener is sized for this application.
People 4 =  300 gallons per day
Hardness =   20 grains per gallon
Iron =              1 part per million (4 gpg of hardness for every 1 ppm of ferrous iron)
PH =            7.4
TDS =         410 parts per million
H2S =          ND
TCH              24 grains per gallon (total compensated hardness)
                 x 300 gallons used per day
               = 7200 grains of total compensated hardness per day.

This application would call for a 45,000 grain softener which would regenerate every 5 days (using 90# of salt per month (7200 grains of soft water are needed for reserve capacity).  A more efficient option would be a 45,000 grain twin tank softener which would regenerate every 6.25 days and would use 72# of salt per month (No reserve capacity required).  The twin tank system would use over 1000# less salt in one year which would save nearly $184.00 per year and also save 1440 gallons of water in that same year. Every company talks about water softener efficiency as it relates to salt usage but VERY few address the overall efficiency which includes salt and water used for the regeneration process.  That is the test of a truly efficient water treatment system.

Summation:  A water softener alone may not always be the solution to every water treatment problem. There are water problems such as high iron content, hydrogen sulfide, low PH, different types of iron and a myriad of other water related issues that may call for additional water treatment equipment to properly treat the water and provide your home and family quality water.
With the proper water treatment system, annual water testing and preventive maintenance you can expect many years of soft, conditioned water which makes your home run more efficiently and improves the quality of living.

Here are some useful links related to this article: 

Good Water, Good Life!

Ray McConnell
Beauchamp Water Treatment and Supply
872 N Old US 23
Brighton, MI 48114

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Water Softeners: How they work
Water Softeners: How they work
Reviewed by Merlyn Rosell
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