fkv, it's great to have experts like you in this community, this is one thing that makes OSM so special. Now, this case looks to me like it is a simple misunderstanding. OSM tags are very often used for a much broader calls of objects than the expert or common definitions of those names. This is to make it easier for applications building on the database, needing to support fewer classifications (and there are already a ton). What experts (or even "normal" people) call a "tunnel" is something different than what the tunnel=* tag in OSM is used for. There is overlap of course, but the OSM tag goes farther than the expert or common definition, and we tag things as "tunnel=*" that are just "similar" to what a "tunnel" usually is. Also, having that tag on it doesn't mean in any way that people can or should enter it. It's merely to say that this way is "housed" in some way and going underneath the ground or large other objects (and not just covered with a roof or similar, which would be "covered"). In this concrete case, if this waterway doesn't have this tag, it would have to be visible on the surface, and I think we can all agree that it isn't. So, the only two options are to not have it exist at all in OSM or to have it marked with the "tunnel=*" tagging, which may not fit the expert definition but it "good enough" for OSM. And yes, any other underground drainage or sewer should have that tagging as well, if it's geographically relevant enough to be in the OSM data set at all.