What Size of Water Softener Do I Need?

Do you find it frustrating when your tanks fail to deliver the desired results due to incorrect sizing? Well, you are not alone! But fear not, we are here to guide you through the process of selecting and calculating the perfect size for your tanks, ensuring optimal performance and maximum efficiency.

multimedia Filter custom

Selecting the Perfectly-Sized Quartz Sand, Activated Carbon, and Softener Tank for You

To choose the appropriately-sized quartz sand, activated carbon, and water softener tanks, several factors must be taken into account. These factors are:

Water usage: The quantity of water used daily is the first consideration, as it determines the size of the tank required to meet the water needs.

● Water quality: The quality of the water also plays a role in determining the tank size needed. For instance, if the water has a high level of impurities, a larger tank may be necessary to ensure effective impurity removal.

● Space availability: It is crucial to consider the amount of space available for the tank, and select a tank that can fit within the space without causing any obstructions.

● Flow rate: The flow rate of the water is another important factor. A higher flow rate necessitates a larger tank.

● Regeneration frequency: For water softener tanks, the frequency of regeneration is a critical consideration. The tank size should be large enough to accommodate the required regeneration frequency without interrupting the water supply.

● Budget: The cost of the tank is an essential factor to consider, and it’s important to choose a tank that meets water needs while also being within budget.

● Maintenance: Ease of maintenance is also important to consider, and it’s best to choose a tank that is easy to clean and maintain to avoid any future problems.

Figure 1 Filter tank measurement.

Calculating The Right Tank Size for You; Examples

Multimedia Filter Tank

A water treatment plant needs to treat 100,000 gallons per day (gpd) of water with a turbidity level of 20 NTU. The desired effluent turbidity level is less than 1 NTU. The filtration rate is 3 gallons per minute per square foot (gpm/sf). What is the perfect size for the multimedia filter tank?


Step 1: Determine the flow rate. The flow rate is 100,000 gpd. To convert to gpm, divide by 1440 (the number of minutes in a day):

100,000 gpd / 1440 = 69.44 gpm.

● Step 2: Determine the filtration area required.  The filtration rate is 3 gpm/sf. To determine the required filtration area, divide the flow rate by the filtration rate:

69.44 gpm / 3 gpm/sf = 23.15 sf.

Stainless steel sand filter

● Step 3: Determine the tank size. The recommended contact time for multimedia filtration is 10-15 minutes. To determine the tank volume required, multiply the required filtration area by the contact time:

23.15 sf x 15 minutes = 347.25 cubic feet.

● Step 4: Convert cubic feet to gallons. Multiply the tank volume by 7.48 (the number of gallons in a cubic foot):

347.25 cubic feet x 7.48 gallons/cubic foot = 2,597.26 gallons.

Therefore, a multimedia filter tank with a volume of 2,597.26 gallons would be suitable for treating 100,000 gpd of water with a turbidity level of 20 NTU, using a filtration rate of 3 gpm/sf and a contact time of 15 minutes.

Activated Carbon Filter Tank

Suppose you are designing a residential AC filter and the average water consumption for the household is 2000 liters per day, and the desired contact time is 10 minutes.

The first step is to calculate the flow rate by dividing the daily water consumption by 24 hours:

2000 liters/day ÷ 24 hours/day = 83.3 liters/hour.

Next, calculate the minimum tank size by multiplying the flow rate by the contact time:

83.3 liters/hour × 10 minutes = 833 liters.

So, the minimum activated carbon filter tank size required for this application is 833 liters.

Figure 2 Water softener tanks.

Water Softener

Example for a household of 4 people: Assuming the household has a water hardness level of 10 grains per gallon (GPG) and an average daily water usage of 80 gallons per person. The total daily water usage for the household would be 80 gallons x 4 people = 320 gallons per day. If the regeneration cycle frequency is every 3 days, then the total water usage between each cycle would be 320 gallons x 3 days = 960 gallons.

To determine the perfect size for the water softener tank, divide the total water usage between each cycle by the water hardness level: 960 gallons / 10 GPG = 96, which means a tank that can regenerate 96,000 grains of hardness would be perfect for this household.

The Importance of Selecting the Perfectly Sized Tank for you

Optimal Filtration

The filtration media such as quartz sand and activated carbon must have enough contact time with the water to remove impurities effectively. If the tank is too small, the water will not have enough time to pass through the media, resulting in poor filtration.


The size of the tank also plays a role in the efficiency of the system. If the tank is too small, it will require frequent replacements or regeneration of the media, which can be costly and time-consuming. Conversely, if the tank is too large, it may use more water and energy than necessary to filter or soften the water.


A properly sized tank will also ensure that the filtration media or resin inside the tank lasts longer. When the tank is too small, the media will have to work harder and may wear out faster, while a tank that is too large may cause the media to degrade due to underuse.

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