Do you have a hard water problem in your area? This simple test will tell you The tester strip is totally harmless, it will measure the quantity of free calcium in your water supply. Dip the strip in a glass of water for 5 seconds. Shake off the excess water and leave for one minute, then see how many squares have changed colour. Each square represents 5 degrees of potential hardness. Whatever the reading, it will be the same after a Water-King is fitted, because none of the calcium is removed from the treated water. 1 degree of hardness = 18mg. of calcium carbonate per litre of water. If you have 10 degrees (2 squares) or over, you have a hard water and limescale problem.