What Size Water Softener Do I Need?
Water softener sizing
It follows your measured hardness, not your square footage
Size depends on two things: how hard your water actually is, and how many people live in the house. Square footage has almost nothing to do with it. The arithmetic is simple. Each person uses roughly 75 gallons of water a day. Multiply that by your hardness in grains per gallon to get how many grains of hardness your household removes daily, then choose a capacity that regenerates about every six to eight days, which is where ion exchange softeners run most salt-efficiently. The reason this matters here more than in most places: hardness in our service area ranges from 3.5 grains per gallon to 23.8 depending on your address. A system sized for the wrong end of that range is either undersized and regenerating constantly, or oversized and wasting salt.
Book a free water testThe capacities we install
We install four whole-house capacities. Grain capacity is how much hardness the resin can remove before it needs to regenerate, so a bigger number means longer between regenerations, not softer water. All four produce water at 0 grains per gallon.
24,000 grains:
One to four people on soft or moderately hard water, up to about 10 grains per gallon. This covers almost every household in Milpitas, Mountain View, Sunnyvale and Palo Alto that needs a softener at all, and most of Los Gatos and Saratoga.
32,000 grains:
The most common fit in Santa Clara County. Three to four people on 11 to 18 grain water, which covers most of San Jose on San Jose Water's groundwater, most of Santa Clara on city wells, all of Morgan Hill, and the well-fed parts of Tracy.
48,000 grains:
Four to five people, or any household on very hard well water above about 19 grains per gallon. This is the right size for Evergreen and Edenvale in San Jose, and for larger households anywhere on groundwater.
64,000 grains:
Five to six people on very hard water, or homes with high simultaneous demand such as three or more bathrooms running at once. Also the right answer at the very top of San Jose Water's groundwater range, which reaches 26.4 grains per gallon.
Sizing by hardness and household size
Capacities below are sized at the top of each hardness band, so they are deliberately conservative. At the low end of a band the next size down is often the better buy. At 3 to 6 grains per gallon, soft to moderately hard: 24,000 grains for any household from two to six people, and honestly most homes at this hardness do not need a softener at all. At 7 to 10 grains per gallon, hard: 24,000 grains for two, three or four people, 32,000 for five or six. At 11 to 14 grains per gallon, very hard: 24,000 for two or three people, 32,000 for four or five, 48,000 for six. At 15 to 18 grains per gallon, very hard: 24,000 for two people, 32,000 for three, 48,000 for four or five, 64,000 for six. At 19 to 22 grains per gallon, very hard: 24,000 for two, 32,000 for three, 48,000 for four, 64,000 for five or six. At 23 to 26 grains per gallon, extremely hard: 32,000 for two people, 48,000 for three or four, 64,000 for five or six.
Worked examples at real local hardness
A four-person household on San Jose Water's groundwater at 16.8 grains per gallon removes about 5,040 grains of hardness a day and needs a 32,000-grain softener, regenerating roughly every six days. The same household in Evergreen, where San Jose Municipal Water's wells average 23.8 grains per gallon, removes about 7,140 grains a day and should go to 48,000 grains. A four-person household in Santa Clara on city wells at 17.1 grains per gallon removes about 5,130 grains a day: 32,000 grains. In Morgan Hill, where all the city wells average 13.7 grains per gallon with no surface blending, about 4,110 grains a day: 32,000 grains. On Tracy's well-fed supply at 15.4 grains per gallon, about 4,620 grains a day: 32,000 grains. And a four-person household in Mountain View on Hetch Hetchy water at 3.5 grains per gallon removes about 1,050 grains a day. At that hardness a softener is usually unnecessary, and we will tell you so rather than sell you one. Hardness figures come from each utility's 2025 water quality report. San Jose Water publishes grains per gallon directly.
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