Looking for impurities in drinking water or other liquids typically involves chemical analysis, which may be time-consuming. Now, however, scientists have created an inexpensive system in which light – that's converted to sound – is used to instantly determine if water is safe to drink.

Being developed by a team at the University of Missouri, the setup utilizes a commercially-available laser tattoo removal machine, which emits a series of 10-nanosecond-long laser-light flashes. These flashes travel down a fiber optic cable, the other end of which is submerged in a small water sample. That end of the cable is also covered in paint-on liquid electrical tape.

In what is known as the photoacoustic effect, the light rapidly heats the tape, causing it to vibrate and emit pulses of sound. The sound waves travel through the liquid, and are detected by a microphone.

By measuring the amount of time that passes between each laser flash occurring and the accompanying sound reaching the mic, it's possible to determine the speed at which the sound waves are travelling through the water. Should the sound not be moving as fast as it would be in untainted water, that means there's something else in the sample, slowing the sound waves down.

"If the water isn't drinkable, then our method will tell you that something is wrong with the water," says Assoc. Prof. Luis Polo-Parada. "For instance, if a facility removes salt from sea water in order for water to be safe for drinking, our method can help alert the facility to potential changes such as an issue with the desalination process."

It is hoped that once the technology is developed further, it could also be used to inspect other liquids – this could include checking for inferior oil diluted into supposedly high-quality olive oil, assessing the quality of liquid honey, or determining the amount of artificial sweeteners or sugar added to soft drinks.

A paper on the research was recently published in the journal Sensors and Actuators, B: Chemical.

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