This is where the math gets a little silly, but it’s actually easy. You need to figure out your daily hardness grain load. First, get a water test kit or call your city—most people have water between 7 and 15 grains of hardness per gallon. That’s like knowing how spicy the salsa is before you take a bite. Then, you multiply that number by the gallons of water your household uses daily (roughly 80 gallons per person, because between showers, laundry, and that one kid who fills the bathtub to the brim, we use a lot of water).
Water Softener Grain Size Calculator at Jaclyn Glenn blog
For a family of four with 10-grain water, that’s 4 people x 80 gallons x 10 grains = 3,200 grains of hardness every single day. That’s a lot of mineral jerks. You want a softener that can handle at least three days’ worth of this nonsense without begging for mercy. So, you’d look for a system that’s at least 30,000 to 40,000 grains. Otherwise, you’ll be refilling salt like you’re a zookeeper at feeding time.
