A health care facility that needs to reduce the hardness of its water supply can estimate the required capacity based on the water usage and the hardness of the water. Water hardness is determined by the concentration of minerals (calcium, magnesium, other) dissolved in the water supply.



(1) current water hardness in grains per gallon or mg per L (parts per million, ppm)

(2) target water hardness

(3) mean volume of water used per day

(4) peak volume of water used per day


grains of hardness that must be removed per day =

= ((grains of hardness per gallon of incoming water) - (target grains of hardness per gallon)) * (gallons of water used per day)



• 1 grain per gallon = 17.12 mg per L

• 1 grain = 64.7989 mg; 1 gallon (US) = 3.7854 liters


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