Biodegradable chelating agents comprising a substituted iminodisuccinic acid having six coordination sites and a simple method for making same are disclosed. A pump between the reservoir of salt water and the interior of the vapor tube generates a pressure differential that forces water vapor from the surface of salt water to the inside of the vapor tube. There is a second electrode located at a second distance from the formation for measuring a second impedance. This flag may also be programmed into the nonvolatile memory device.