COM-100 USER’S GUIDE ADDENDUM FREQUENTLY ASKED QUESTIONS (FAQs) MODE SELECTION GUIDE What should the TDS of my water be? A TDS level is specific for each application and particular usage. If you are using the COM100 to test the water pertaining to a particular device, object or operation, contact the manufacturer of that object. For example, if you are using the COM-100 to test the efficacy of a water filtration system, contact the manufacturer of that system for preferred TDS levels.