This technology was developed by Kansas State University in the early 1970s. Proven to be a highly effective and practical means of purifying water, NASA chose to use the iodinated resin technology in the Space Shuttle program. Iodinated resin releases the iodine necessary to kill the microorganisms that are actually present in the water. Because penetration of the microorganism is so effective, contact time is minimal and iodine concentration levels remain low. In comparison, using straight iodine leaves 60 ppm of residual iodine in the water.
Most systems have carbon as the final stage.
This carbon stage absorbs residual iodine. Once you notice this taste shift it is time to replace the purification cartridge. It is still purifying the water at this point but you will want to install a new cartridge as soon as possible in order not to exceed the effective life of the cartridge. The sediment stages of the systems should be replaced whenever their rated capacity is reached or when they have collected enough sediment to reduce the water flow. A good rule of thumb is to figure a gallon per person per day for cooking and drinking purposes.