Natural waterways are distinguished by their size (jump over width) as being a river or a stream which makes sense although this distinction is a bit vague.
For man made freshwater channels we only have one tag “canal”, although these waterways can also be tiny (< 30 cm) or huge (> 10 m). As most people do not understand a tiny channel to be a “canal” this leads to mistagging of small man made freshwater channels as “stream” or “drain” which are both not correct.
A good example are mill races which can be found in many places although the mills have ceased operating sinse long. Such mill races are man made and often in between 0.5 to 1.5 meters wide (easy to jump over). They are no streams as they are not naturally formed and they are no drains as they do not carry superflous or waste water.
The same applies to small channels like the “Freiburg Bächle” which are actually tagged as “drain” which they definitely not are.
To distinguish these small freshwater channels from big canals for shipping etc. I would appreciate to have a separate tag (similar to “stream”) for those being not too wide to jump over.
In my area, we call irrigation channels “canals” (usually too wide to jump over, too narrow and shallow for a boat) but I don’t tag them as waterway=canal since I understand that to mean a wider, navigable feature.
Have you looked at waterway=ditch for something like this? The wiki is a little inconsistent in what that means but I find it closer than canal for these little man-made waterways.
Part of the issue here is the orthogonality between the construction of a waterway and the use of a waterway. A small (artificial) waterway can have surprisingly many functional/decorative/natural uses, and be dug/built in many ways. Often waterways built using the exact same techniques serve very different purposes.
With the relatively few waterway= tags in use (drain, stream, ditch, ++), it is clear that many different things have been grouped together using some shared characteristics.
Agreed, I might even go as far as to say that in an ideal world waterway= would describe the overall general physical nature (width, depth, perhaps typical flow rate) and other tags would drill down into the details like lining, purpose, construction, etc.
Agreed, this is the pragmatical aspect of mapping small waterways. Most mappers do not want to waste time to measure width, depth and flowrate of a small water channel nor of a stream or river and that is why we have more generic tags for those.
Under this aspect those tags in use make sense to me:
