The manufacturer warranty on water treatment systems will vary widely,depending on the type of system, and the brand. There are no absolute rules, but generally, the less expensive the device, the shorter thewarranty. In other words, a point-of-use carbon filter will probably not be guaranteed for as long as a whole-house reverse-osmosis system. Magnetic water conditioners tend to have some of the longest warranties, probably because they have fewer parts to wear out. These guarantees can run from ten years, to a lifetime. Whatever the device, if it should fail within the warranty period, most manufacturers will either replace it, repair it, or refund your money. However, this decision is usually made at their discretion. Certain systems may require you to use the product for 90 days, before judging its final effect. Then, if not satisfied, you generally have another 30 days to return it. The more money you’re going to invest, the more important the warranty becomes. You can improve your chances by simply choosing a product with a reputation for reliability. Consumer publications, trade journals and other independent studies can be a good source of such information. Finally, always keep your sales receipt, and a written record of any customer service calls.