Water Softener Sizing

In order to properly size the water softener unit you need, some known factors regarding the incoming water to be softened are required. These calculations presume you have tested your incoming water to know the following:

  1. Hardness Rating: expressed in grains of hardness per gallon
  2. The level of Iron: expressed in PPM (parts per million) or M/L (milligrams per liter)
  3. The level of Manganese: same expressions as per iron (PPM or M/L)

The only other factor needed to size your water softener is to determine the population served by the unit. Typically, this is the number of permanent residents (adults and children) in the household.


1. Calculate DEMAND — Start by multiplying the population served times 80 (for general calculations, figure 80 gallons per day water usage per person). Example: a 4-person household would calculate to 320 gallons per day demand.

2. Add 2x the tested Iron level to the tested hardness value. Example: Hardness level test results = 10.
IF that included 0.5 ppm iron. Add 1 grain (2 x 0.5 = 1) to the hardness value.

3. Add 2x the tested Manganese level to the tested hardness value. Example: Hardness level test results = 10. That included 1 ppm of manganese. Add 2 grains (2 x 1 = 2) of hardness value.

Summary example of steps 2 and 3 above: 10 + 1 (for the iron) + 2 (for the manganese) Calculated Equivalent Hardness Value = 13.

4. Multiply DEMAND by the Calculated Equivalent Hardness Value. This will give you the GRAINS PER DAY figure. Example: 320 gallons times a Calculated Equivalent Hardness Value of 13 = 4,160 grains of hardness per day.

5. It is most economical to size  your water softener so that it does not need to regenerate more often than once a week. So, multiply the calculated grains of hardness per day by 7. As per example above: 4,160 grains x 7 = 29,120 grains per week.

In the example above, the H2O-M2010 (30,000 grain) water softener would be the properly sized unit. Capable of accommodating 29,120 grains of hardness removal per regeneration.

NOTE: If your water tests over 1 ppm for Iron, you should consider iron removal pre-treatment technology. Contact ESD at 602-649-3050 or Sales@esdwater.com to discuss iron removal.