Why does toilet water move when it’s windy outside?

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I live on a condo and noticed that the water in the toilet bowl was slightly moving (kinda like waves) and was fascinated. So i started paying attention to it more and noticed that it would do that only on windy days, the windier it was, the more it moved and would sometimes start to resonate which blew my already blown mind!

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There is a vent that goes through your roof and is connected to your plumbing drains. It facilitates the water draining to the sewer or septic. Wind blows over it and creates oscillations in the connecting plumbing.

Interesting. I’ve never noticed this! Now I’ll be staring at my bowl when there is a wind storm. If I had to hazard a guess it may have to do with the air pressure difference between outside and inside sort of like a barometer. Or it could be your building is slightly shifting in the wind depending on how tall it is.

[This is the typical sewer pipe setup](https://www.repipeyourhouse.com/wp-content/uploads/2018/11/i-3-1.png).

The water in your toilet bowl and in the U pipe under your sink prevent the sewage smell gases from getting into your rooms. However, these gases must be released or pressure will build up, so there’s a pipe vent going to the roof. So when the wind blows strongly outside, there’s a bit of a [chimney effect](https://en.wikipedia.org/wiki/Stack_effect) and some of that atmospheric wind “pressure” pushes on the water in your toilet bowl a little bit, enough to create waves.