[Tagging] How to tag small canals?

[SelfishSeahorse]

Hello

What is the usual (or sensible) way to tag small canals like mill
races (example: [^1]) or small irrigation channels (example: [^2]),
i.e. the small equivalent of waterway=canal?

[^1]: https://commons.wikimedia.org/wiki/File:15-19-077,_mingus_creek_-_panoramio.jpg
[^2]: https://commons.wikimedia.org/wiki/File:2003-Suone.jpg

It seems to me that waterway=ditch +
usage=headrace/tailrace/irrigation fits best, but the wiki defines
waterway=ditch as 'a small man-made draining waterway, often found
along roads'.

Regards

Markus