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Science

How to switch your dripping tap to 'silent'

Darko Janjevic
June 22, 2018

We have all heard the irritating plink-plink sound of a dripping water faucet in the middle of the night. Now, Cambridge scientists have determined what causes the noise and found a simple way to render it silent.

https://p.dw.com/p/306we
Drops of water falling from a tap
Image: picture-alliance/dpa/C. Schmidt

A group of researchers from the University of Cambridge in the UK has published a study on the sound of dripping water, discovering exactly how the noise of a drop of water hitting a container filled with liquid is generated.

According to the scientists, the sound does not come from the impact of liquid on liquid. The splash, the momentary cavity formed by the impact, and the jet of water shooting up are all "effectively silent," the researchers said. Instead, the source of the noise is a small air bubble that forms at the bottom of the cavity. The trapped bubble then acts "like a piston," forcing water to oscillate and driving sound waves into the air.

"Using high-speed cameras and high-sensitivity microphones, we were able to directly observe the oscillation of the air bubble for the first time, showing that the air bubble is the key driver for both the underwater sound, and the distinctive airborne 'plink' sound," said PhD student Sam Phillips, one of the authors of the study, according to an article published on University of Cambridge website on Friday. The university also published a Youtube video based on the study.

Read more: Germans turned off by tap water

Add dish soap

Lead researcher Anurag Agarwal of Cambridge's Department of Engineering said he decided to look into the problem while visiting a friend who had a small leak in the roof of his house. Agarwal works in the field of acoustics and aerodynamics of aerospace, domestic appliances and biomedical applications. "While I was being kept awake by the sound of water falling into a bucket placed underneath the leak, I started thinking about this problem," he said.

Read more: German man runs up enormous bill by letting taps run

Most importantly, the scientist discovered an easy way to silence the noise. Adding some dish soap, also known as washing-up liquid, to the container is enough to change the surface tension and eliminate the sound.

The findings of the study were published in the Scientific Reports magazine.

The scientists say they were motivated by curiosity, but added that the findings could be used to measure rainfall or improve sound for water droplets in movies and video games.