Yes, it is considered hard water in our area. The South Platte River serves as the Highlands Ranch's main source of drinking water. This water source contains calcium and magnesium, two minerals that are common in hard water. How soft or hard your water really depends on how many grains of these minerals are present per gallon. The water levels at Centennial Water typically range from 11 to 13 grains per gallon (188 – 222 milligrams per liter). Hard water is 9-18 grains per gallon.