Groupon has the Lifestraw Personal Water Filters at a special $14.99 price – almost $5 less than Amazon!  Since it contains no chemicals, it has no expiration date.

Award-winning LifeStraw has been used by millions around the globe since 2005
Removes minimum 99.9999% of waterborne bacteria (>LOG 6 reduction) and surpasses EPA standards for water filters
Removes minimum 99.9% of waterborne protozoan parasites (>LOG 3 reduction) and filters to an amazing 0.2 microns
Filters up to 1000 liters of contaminated water WITHOUT iodine, chlorine, or other chemicals
Comes in a sealed bag, perfect for storing for emergencies