Space Station Freedom's potable water recycling system will use iodine biocide. A process control water quality monitor will continually measure potable water parameters, including the 2.0 to 6.0 mg/l iodine concentration range. The iodine sensor will be a photometric flow cell that measures iodine's 465 nm radiative absorption band and reports iodine concentration. The expanded ECLSS Preliminary Operational System Test included prototype iodine sensors. A solid state iodine sensor will meet power, weight, reliability, and maintainability requirements associated with the station's redesign. This paper discusses solid state photometric iodine measurement theory and engineering considerations and presents preliminary LED-based sensor test results.