Briefly explain the importance of optimal fluoride concentrations in drinking water. at which point during the water purification process should fluoride be added to the water? (6) what is the reason for adding fluoride at this particular stage? a home water softener has 75 000 cm3 of ion exchange resin with a capacity of 39 kg/m3. 3.3 the occupants use 1800 l/day of water containing 0.24 mg/cm3 of hardness as cacoa. if they want to soften the water to 78 mg/l as caco3, what percentage of water should bypass the unit? when will the unit need to be regenerated?