[Tagging] Storm attenuation ponds

[ael]

I am uncertain how to tag the sorts of flood defense storage ponds
that seem to be required in most current construction sites.

I have used 

landuse = reservoir
reservoir_type = flood_defense

for now, but I feel that some sort of water tag ought to be present as well.
Erm, natural = water ? I guess the water is natural, even if the pond is
artificial. That and water=storage_pond; covered=no ??

Ugly.

Is there a good solution to this common situation?

ael