TDS creep is a term used to describe the normal process which occurs when your RO/DI system is turned off. When the system is not running, the rejected high TDS water surrounding the outer core of your RO membrane equalises with the ultrapure water inside the membrane’s inner core, raising the TDS to levels that are usually above 80 ppm in TDS. When the system is then turned on, this high TDS water floods your DI resin, shortening its life unnecessarily.