Surface tension creates a glassy, smooth layer of water over U.S. swimmer Tyler Clary the instant before he surfaces as he competes in the backstroke. Surface tension arises from intermolecular forces between water molecules.

In 2007, the Department of Water Protection in Los Angeles detected high levels of bromate, a carcinogen that forms when bromide and chlorine react with sunlight, in Los Angeles's Ivanhoe Reservoir. Bromide is naturally present in groundwater and chlorine is used to kill bacteria, but sunlight is the final ingredient in the potentially harmful mix