Adding fluoride to water has been common practice in a number of countries, including India. In low concentrations, it can help prevent tooth decay and even strengthen bones, but going above that can have the opposite effect. Scientists have developed a portable and user-friendly device that can measure fluoride concentration accurately using only a few drops of water, and help address contamination in drinking water, said researchers from the Ecole Polytechnique Federale de Lausanne (EPFL) in Switzerland.