Calgary is going to start fluoridating our drinking water to prevent tooth decay. Health Canada's Guidelines for Canadian Drinking Water Quality set a maximum allowable concentration of fluoride ions to 1.5 mg/L (F-). The presence of calcium ions in hard water can precipitate the added fluoride. What is the maximum molarity of calcium ions in hard water if the fluoride concentration is at the Health Canada's maximum allowable level? (Ksp for CaF2 = 4.0 10-11)