How To Size A Water Softener

Getting the correct water softener for yourself is a decision you should make based on your water type and your water usage.

It is advisable to get a water softener in areas that have hard water. You know you have hard water when there is white or grayscale buildup on your pots and pans, or when your clothes have a layer of detergent film post-wash. Some even claim that hard water affects your skin and hair adversely.

When you ask yourself the question, “Do I need to get a water softener?”, it helps if you know what hard water or soft water is, and how the treatment of hard water takes place to give you soft water, as well as if you have any use for it.

  1. Hard Water and Soft Water
    1. Water Hardness Classification
  2. Water Softening Process
    1. Ion Exchange
    2. Regeneration
  3. Sizing a Water Softener
    1. Water Hardness
    2. Water Consumption
    3. Daily Softening Requirement
  4. Types of Water Softeners
  5. Maintenance

Hard Water and Soft Water

Your water’s hardness or softness is dependent on two highly soluble minerals that are usually found in water. These two minerals are magnesium and calcium, which are generally beneficial for our health. These two minerals are also responsible for the difference in the taste of water in different regions.

Magnesium and calcium—when present in the water—also cause buildup on surfaces. This leads to blocked pipes and damaged water heaters. A significant quantity of these minerals also makes soaps and detergents feel less soapy and less effective.

This is what we know as “hard water”.

Water Hardness Classification

There are two units of measurement to express water hardness—parts per million or ppm, and grains per gallon or gpg.

One part per million (ppm) of calcium carbonate in water is equivalent to one unit of calcium carbonate dissolved in one million units of water. Here, calcium carbonate is a term we use to represent the concentration of dissolved calcium or magnesium.

Grain per gallon (gpg) of calcium carbonate is the other measurement that is used exclusively to represent the hardness of the water.

A water testing report will use either one or both of these measurements to classify the hardness of your water.

  • When the concentration of calcium carbonate in water is less than 1 gpg or less than 17 ppm, your water is soft and you do not need a water softener.

  • When the concentration of calcium carbonate is 1.0–3.5 gpg or 17–60 ppm, the water is slightly hard, and you can make do without a water softener if the water hardness does not affect you adversely.

  • When the concentration of calcium carbonate is 3.5–7.0 gpg or 60–120 ppm, the water is moderately hard.

  • When the concentration of calcium carbonate is 7.0–10.5 gpg or 120–180 ppm, the water is considered hard.

  • When the concentration of calcium carbonate is greater than 10.5 gpg and 180 ppm, the water is considered very hard. This water causes a lot of damage to property, which is a hassle to clean up after.

Water Softening Process

Depending on the water hardness level, you can decide to get a water softener. But are you aware of the processes involved in this magical transformation of water?

The biggest step in this transformation is ion exchange.

Ion Exchange

A water softener is also known as an ion-exchange unit since the exchange of ions is what changes hard water into soft water. In this process, the water is treated so that the levels of magnesium and calcium are reduced.

An exchange media called resin is used to filter the hard water. Resin, also known as zeolite, is a synthetic or natural material with the texture of sand. It is coated with sodium ions that are positively charged.

When the hard water is passed through the resin, a physical and chemical filtration process takes place. The magnesium and calcium of the water dissolve into the positively charged sodium ions. This creates an environment for ion exchange as the resin releases the sodium ions and replaces them with the calcium and magnesium ions.

The water comes out soft after this filtration process.


After going through multiple cycles of softening water, the positive ions in the resin responsible for softening the water are depleted. It is necessary for the water softener to go through a process called regeneration for it to continue functioning effectively.

Regeneration is an alternate cycle with a salt solution that is used to restore the positive ions in the resin. The magnesium and calcium are washed out of the resin when backwashed with the brine solution.

This process is automatic in some water softeners while it is manual in some. You can get either of the two based on your usage of the water softener.

Sizing a Water Softener

To properly size a water softener for your use, you need to consider two major factors—water hardness and water consumption.

Water Hardness

As discussed in detail previously, water hardness is measured by how much magnesium and calcium is dissolved in your water. It is important to know the exact hardness of water to prevent getting yourself an improperly sized softener.

The system also asks for the water hardness level while being programmed. Hence, an improper value will cause misuse of your fairly expensive device.

You can get a test done on your water to determine its hardness or get the value from your local water utility if you are on city water.

Note that the presence of iron in water increases its hardness. 3 gpg of hardness is added to the total value of water hardness for every 1 ppm of iron.

Water Consumption

Your daily softening requirement also depends on how much water you consume on a daily basis. You can calculate how much water you use per day by multiplying the number of people in your household by 75 gallons. It gives a fair estimate of the daily water usage in a household.

Another convenient and more accurate way to do this would be to check your water bill. You can calculate how much water your household uses daily from the total water consumption over a given period of time.

Daily Softening Requirement

Calculating your daily softening requirement is super easy once you have the two abovementioned values with you.

Here is an example of how to calculate your daily requirement:

Let us assume you have a household of 4 people, and each person uses 75 gallons of water on average per day. The value of water hardness is 10 gpg.

Water usage = 75 gallons/day x 4 people = 300 gallons/day

Softening requirement = 300 gallons per day x 10 grains per gallon = 3,000 grains/day

In this scenario, there is a requirement for a water softener that will take out 3,000 grains per day.

Based on this information, you need to calculate and select a water softener that will serve your purpose. Buying a device that is underused is as much a waste of money as one that is overused.

You also need to keep in mind that not all your water usage requires soft water unless your water is extremely hard. For example, you can arrange your water distribution in such a way that you get softened water for your sinks, showers and laundry hookups and use unsoftened water for toilets and water outlets outside the house.

This way you use your water softener judiciously and save a significant amount of money.

Types of Water Softeners

There are various different brands and models of water softeners available on the market, but they all perform the same function of ion exchange, barring some minor differences from model to model.

There are two categories of water softeners—timed models and demand-control models.

  • Timed models include a system where the process of regeneration takes place automatically at a scheduled time, following which the water softeners resume functioning.

This is a very convenient option and a good investment for households where there is a regular water-use cycle.

In this type of softener, the process of regeneration would take place irrespective of the resin needing it. This means more water and salt wastage.

  • Demand-control type of water softener models has either electrical or mechanical sensors that trigger regeneration only after a certain amount of water is softened. This model is convenient for households where the usage of water is not scheduled.


The purpose of any water softener is to maximize soft water quantity while using minimum salt from the resin. For this, it is necessary to keep your water softener well-maintained.

Always keep a well-mixed brine solution in the brine tank. The resin also tends to get clogged occasionally if your water is especially hard and dirty. You should keep an eye out for such a situation.

If it is a regular occurrence, you can set up a filter for your water to remove other impurities before it goes through the process of softening.

A clogged resin is usually well-dealt with the regular backwash with brine water. But in case it does not clear up, slowly stir the resin during the regeneration cycle to break up the impurities.

Sometimes bacteria and fungi grow and reduce the resin’s effectiveness. This can be dealt with by disinfecting the water before it passes through the softener or treating the softener periodically using a mild chlorine wash.

Sometimes the resin can be damaged to the point where backwashing cannot restore it. In such a case, you might have to replace the resin. Your water softener dealer will be able to help in this scenario.

Before taking any of these maintenance steps, read the manufacturer’s instructions well.

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