It's important to remember the water does NOT actually move in a wiggle like that.
Obviously it's impossible for water to change directions like that without something pushing it.
Instead the end of the hose is shaking, causing some water to flow on the left of the screen, and some on the right.
The water moves straight down! But it's in bursts.
But if you time the camera right you catch the bursts always in the same place, and it looks like a zigzag.
Imagine a piece of paper being pulled, and a pen wiggling back and forth. The paper (i.e. the water) moves exactly straight. But the motion of the pen (i.e. the hose) makes it look like a zigzag, but each portion of the paper only moves straight.
Obviously it's impossible for water to change directions like that without something pushing it.
Instead the end of the hose is shaking, causing some water to flow on the left of the screen, and some on the right.
The water moves straight down! But it's in bursts.
But if you time the camera right you catch the bursts always in the same place, and it looks like a zigzag.
Imagine a piece of paper being pulled, and a pen wiggling back and forth. The paper (i.e. the water) moves exactly straight. But the motion of the pen (i.e. the hose) makes it look like a zigzag, but each portion of the paper only moves straight.