Celebrity scientist Dr Karl reveals how you might ‘be brushing your teeth with toilet water’

Apr 09, 2022

Australian author and celebrity scientist, Karl ‘Dr Karl’ Kruszelnicki, has taken to social media to educate fans about the proper way to flush a toilet.

In the video, posted to social media platform TikTok, Dr Karl explained the various hygiene concerns associated with flushing the toilet with the lid up.

In the video, Dr Karl asked fans “what happens if you flush the toilet with the lid open?”, before revealing its rather disgusting reality.


Do you need scientific evidence to make your housemates flush with the toilet lid shut? Here you go 😎 #drkarl #drkarlkruszelnicki #science

♬ original sound – Dr Karl

“If you flush the toilet with the lid up, a polluted plume of bacteria and water vapour just erupts out of the flushing toilet bowl,” he said.

Dr Karl went on to explain how the water particles produced in the flushing “eruption” then float around in a person’s bathroom before eventually landing around the room.

“And some could even settle on your toothbrush!” he said.

“So if you flush with the toilet lid up, you could be brushing your teeth with toilet water.”

Dr Karl ended the video with a cheeky jab at the male audience’s toilet habits.

“I guess that’s one way to get the males in your house to put the toilet lid down,” he joked.

Dr Karl uses TikTok to share regular educational videos with fans where he reveals light science “truths” to thousands of social media users.

In previous videos, Dr Karl explained the science behind a number of long-debated topics, such as “What happens to fart when you hold them in?” and “Does cracking your knuckles give you arthritis?”


Does cracking your knuckles cause arthritis? Post your questions in the comments and if you want more science, head to my podcasts! #drkarl #science

♬ original sound – Dr Karl

Kruszelnicki is a well known science commentator on Australian radio and television. He graduated with an honorary doctorate in medicine from the University of Sydney in 1986 and over the years has secured himself a well-known, trusted educator of science.

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