[UPDATE] Purchased another in September 2018 with Expiration in December 2022.
Inexpensive but need to check the expiration date, which is NOT printed on the package. This requires opening the main package to examine each individual tablet package. If you received a recent or newer package you should have 4 to 5 years before the expiration date. However, as a water purifier, this is far better in taste than iodine but one needs to plan and be patient, since it take 4 hours to kill the bugs before use.