ELI5: Explain Like I'm 5

Inverted siphon

So, imagine you have a really, really long straw. Now, we all know that when you drink from your straw, you have to make sure there’s air and liquid in it for it to work, right? Well, the same goes for a really long straw, except the straw is super, super long and also it's underground.

Sometimes, when we need to move water from one place to another, we can’t just have it run on the surface, so we have to bury a really long pipe underground to carry the water. And sometimes, the pipe is going uphill or over something like a valley or a river, which can be a problem since water naturally wants to flow down, not up.

This is where an inverted siphon comes in. An inverted siphon is just a fancy way of saying that part of the pipe is turned upside-down. So, instead of the water trying to go up the hill or over the valley, it goes down into the upside-down part of the pipe and then comes back up the other side!

It’s kind of like when you’re trying to get the last bit of milk out of your cereal bowl with a spoon. You turn the spoon upside down and dip it down into the milk to get the milk to stick to the spoon and then bring the spoon back up to your mouth.

So an inverted siphon is like a really long straw that dips down into a low spot before it goes back up again to keep the water flowing in the right direction. That way, we can move water from one place to another even if there’s something in the way, like a big hill or a river!