Despite your advice, many contact lens wearers continue to clean their lenses with tap water or bottled water. Here’s ammunition you can use when you’re trying to persuade them to follow your wise instructions.

Researchers at the Baylor College of Medicine in Houston, Texas, tested two samples of 23 brands of noncarbonated bottled water sold in grocery stores. Though many people perceive bottled water as being cleaner, the scientists found that 48% of the brands they tested contained microorganisms such as bacteria, yeast, mold or amoebas. Thirty percent tested high for coliform bacteria, which indicate pollution with human waste or animal waste.

The water was sold as "spring water," "glacier water," or "drinking water." Fifty percent of the "drinking water" samples contained contaminants, compared with 33% of the "spring water" samples. Forty-three percent of the "drinking water" samples contained bacteria or coliforms compared with 13% of the "spring water." Both samples of "glacier water" contained bacteria. Overall, 12 of the 23 brands contained no bacteria or fungi, but in six brands both samples of each tested were contaminated.