To choose the softener with the correct capacity, water usage and water hardness must be determined. Water usage can be obtained from a water bill, or use the estimated 100 gallons per person per day average for most US citizens. Water hardness information can often be obtained from the local water company. Water should be tested in a well water system, or when the local municipal water information is unavailable. Use Vertex Hardness Testing Strips for quick onsite testing, or contact an independent lab through the Water Quality Association (WQA) or local Department of Health.

Example:
An average family uses 100 gal./day of water per person. A household of four needs 400 gal/day of softened water. If the water has a hardness of 20 grains per gallon, 8000 grains have to be removed per day (400 gal. X 20 grains/gal.) With regeneration every 3-days, the minimum softener capacity should be 24,000 grains (8000 grains/day x 3 days). A 1.0 cu. Ft. softener model can remove 30,000 grains and would be the right choice.

Hardness conversion
Hardness is measured in grains per gallon (GPG). Most often the published municipal water information is in part per million (PPM). Determine the GPP by using the equation:

PPM ÷ 17 = Grains per Gallon (GPG)