A spout is a tube-like structure which allows liquids to flow from one place to another. A teapot, a jug and a kettle all have a spout. This is where the water flows out of the vessel. A waterspout is a pipe that runs down from your roof to the ground that allows rainwater to flow down from the roof so it doesn't become damaged. So the ant (or the spider in the rhyme I know) climbs up that pipe. It's pretty clear.

For a native speaker, "water spout" is likely associated with a water pipe or a drainpipe, especially because of the famous children's song "The Itsy Bitsy Spider", where the spider climbs up a "waterspout." The word "waterspout" traditionally refers to a pipe or structure that directs water away, such as a drainpipe on a building. Over time, especially in nursery rhymes and casual usage, it became synonymous with a vertical pipe for water drainage. This cultural context likely influences why "waterspout" brings to mind a pipe rather than, say, a natural whirlpool or tornado over water, which is its other meaning. So, the association comes from cultural context and language evolution, not strict logic.

Hi Robson, This is because of regional differences in the words. A waterspout is a word used to mean 'water pipe' or 'downpipe' in the UK. It's not super common anymore in my experience. Hope this helps!

I think it’s the name of a product you can buy to fit over a tap to create a spout of water effect

I've always heard the Itsy Bitsy Spider song with a spider, not an ant. It is an old song as is the old word "waterspout". This is the image I think of