It’s important to determine the size of water softener, otherwise you’ll be underserved by the system. The general rule is, multiply the number of inhabitants in your house with the average water consumption in gallons. (Usually, it’s 80 gallons).
Now, again multiply that number with the grain of hardness found in your water. This way, you’ll get an estimation of how much grains need to be removed every day. Now, look for a system that can handle the requirement. Usually, a four-person household needs around 33,000-grain softener unit.