When traveling, it's smart to make sure that your water is safe no matter where you go. The SteriPEN by Hydro-Photon Inc. uses ultraviolet light to kill 99.99 percent of waterborne viruses, bacteria, and protozoa -- including E. coli , dysentery, cholera, influenza, hepatitis, salmonella, and giardia -- in about 60 seconds. It's the same type of technology used by many US spring water bottling plants, and this portable version lasts for about 5,000 treatments, according to the manufacturer. It is for use with clear water only, as the device does not remove sediment. It weighs about 8 ounces, is 7 inches long, and runs on four AA batteries(the NiMHrechargeables last longest, but the device can disinfect an estimated 20 to 40 16-ounce glasses of water using standard alkaline batteries). The UV lamp comes on automatically when immersed in water, and the SteriPEN fits most standard drink bottles. It costs $129.95 at Hilton's Tent City , 272 Friend St., (800-362-8368) or $99.95 through the Herrington catalog (www.herringtoncatalog.com; 800-622-5221 ) and also online at rei.com, backcountrygear.com, and magellans.com.