What Size of Water Softener?
Household water softeners are rated by the number of grains of hardness they can remove through a specific volume of resin in the tank, and the amount of salt needed to regenerate the resin. To find the right size of softener for your household you will require two things:
Your average daily household water use not including outdoor watering
The average grains per gallon of hardness in your tap water
1. Calculate your Average Daily Household Water Usage
Method 1: The average person consumes between 167 and 195 litres (44 and 51.5 US gallons) of water per day, respectively. Consider your water usage characteristics and use 50 gallons if you are unsure. To calculate your daily household water use, multiply your average per person water use in gallons by the number of people in your household.
ie: 4 people x 50 gallons = 200 gallons per day.
There is no need to add a person to your calculation for dishwashers.. Households with dishwashers use less water than households washing dishes by hand!
2. Find the Water Hardness
Water hardness is measured as grains per U.S. gallon (1 grain = 17.1 milligrams per litre). Residents connected to municipal water supplies can find their average water hardness by contacting their local municipality.
Iron Considerations
If you are on a private well, you will need to have your hardness and iron tested separately in order to calculate your hardness rating. You may need to increase your grain hardness rating to compensate for iron in your water. For every one (1) mg/l (milligrams per litre) of iron, three (3) grains per gallon (gpg) of hardness needs to be added to the total hardness value.
Test for water harness annually to detect any changes in your water quality
Calculate your Daily Hardness Removal Requirement
Multiply your households average daily water use as calculated in step one, by the grains of hardness in your water found in step two. To calculate your daily hardness removal requirement:
Ideally a water softener should remove hardness from the water for seven days before needing to regenerate. Simply multiply your daily hardness removal requirement by seven to calculate the suggested water softener size. Although water softener sizes vary, the table below gives some of the more typical sizes of softener available for a range of daily grain requirements.
Daily Grain Requirements Suggested Softener Size
0 - 3,500 grains per day 24,000 grain capacity
3,501 - 4,500 grains per day 32,000 grain capacity
4,501 - 5,750 grains per day 40,000 grain capacity
5,751 - 6,850 grains per day 48,000 grain capacity
Using the formula above, a family of three using 60 gallons of water per person per day, with a water hardness of 23 grains per gallon, will need a softener that can remove 4,140 grains of hardness per day. Over seven days, the softener would need to remove 28,980 grains of hardness. The suggested softener size for this family would be one with a 32,000 grain capacity.