Tag:historic=watermill
 historic = watermill
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A historic mill using the power of water in its production process. 
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| Group: historic |
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| Status: in use |
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The tag historic=watermill can be used to map watermills which are out of use, but for which physical remains are still visible above ground. It can since have been assigned a new use such as a tourism=museum or retail (shop=* or amenity=restaurant) space which should be mapped separate.
The local name or label on old maps is usually derived from the product=* (such as "Corn Mill" or "Flour Mill") rather than the power source, in contrast to how we map on OpenStreetMap. See below for suitable tags for the product of the mill. A watermill will be located near a waterway=stream, waterway=river or mill race. The mill race might however be filled in now.
How to map
Depending on the state of the building and whether there is just one mill building or a complex of buildings, map as an area or a building relation with several building parts. The tag man_made=watermill is more common, but might not cover the historicity of the structure sufficiently. If the mill is no longer in use, you may use a lifecycle prefix such as disused.
If the mill has a name (sometimes after the location or the last miller), this can be mapped with the key name=*, historic:name and/or name:YEAR.
Add the usual tags available for buildings such as
Add wiki tags such as
Add other image sources such as
Many watermills are protected buildings, so you can add heritage tags such as
heritage=*ref:IE:niah=*for mills in the Republic of Ireland
To specify the former product=* of the mill, you may use historic:product=*. This often changed during the history of the mill, depending on demands (from woollen mill to flour mill, for example), so it might be useful to use semicolons between the products (ideally in chronological order) or dates, according the available sources, for example product:1839=wool or product:1839-1880=cut_stone. For Ireland and the United Kingdom, the old Ordnance Survey maps available as layers in JOSM and on maps.nls.uk are useful resources (see below).
You may want to add a description=* for anything you cannot cover in one of the suggested or other tags.
A tag for mills which are tourist attractions can be used on a separate node 
(tourism=attraction - see One feature, one OSM element). This might also require contact details etc. to be mapped.
Mappable items around the watermill
If the watermill is still associated with a waterway=*, make sure that it is mapped.
If the waterwheel is still in place, it can be mapped as a node or way 
with the man_made=waterwheel. In addition, it might be of interest whether the wheel is undershot (where the water hits the water at the bottom) or overshot (where the water hits the wheel from the top) which could be mapped as waterwheel=undershot or waterwheel=overshot.
Most waterwheels are now vertical, but the two alternatives could be mapped with waterwheel:orientation=vertical or waterwheel:orientation=horizontal.
Information panels, commemorative plaques etc can also be mapped, see tourism=information.