This story is offered because I find it interesting, and as a possible catalyst for updates to our tagging documentation. I offer apologies to those that are well aware of this controversy.
There are two competing ways to tag reservoirs: landuse=reservoir, or natural=water + water=reservoir. The reservoirs near me all used the "landuse" version, and so I only recently became aware of the difference when another mapper pointed it out. landuse=reservoir was the original scheme (first documented on the wiki in 2008), while water=reservoir came about three years later, in an approved 2011 proposal[1] which added the key "water". To read the voting commentary, the proposal was mildly controversial: one user described the vote as rushed, and another cited an issue we still discuss in 2020: whether there is a difference between water=lake and water=pond! The proposal noted among other things that "landuse=reservoir [is replaced] by natural=water + water=reservoir". It further went on to state: "Until all renderers (which render those areas differently from natural=water) support those new values, both schemes can be used together: just add natural=water and water=* to already present tags." And so, mappers began mappers began adding the new tags to the map. In mid-2011, landuse=reservoir sat at 180K usages while the newly-invented water=reservoir had near-zero usages. The proposal described that mappers should use both tagging schemes until renderer support was achieved, after which (presumably) landuse=reservoir could be safely removed from these features (and we could finally stop tagging something that is in reality a type of water as a type of land!) Renderer support for natural=water is ubiquitous today. However, there was no trigger built in to declare that "renderer support has been achieved", and the double-tagging went on for *eight years*. By the end of 2018, tagging of landuse=reservoir had peaked[2], having racked up 450K usages. The upstart water=reservoir, while still far behind, had been experiencing a near-exponential growth curve[3], with 180K usages. 2019 was a turning point, and over the last two years, landuse=reservoir has been on a steady decline, while water=reservoir continued its rapid growth. As of today, landuse=reservoir is down to 384K usages, and water=reservoir has reached 332K usages. However -- if we exclude nodes (as there are a large number of presumably imported landuse=reservoir nodes still hanging out in the map), water=reservoir is slightly ahead - 331K vs 330K. Now let's turn to what our wiki has to say about this: "There was considerable confusion whether landuse=reservoir is deprecated, but it turned out to be not deprecated and landuse=reservoir is used more widely than "new" way natural=water + water=reservoir." This is...an interesting lede for a tagging article to say the least! The real story behind this awkwardly-worded statement is in the landuse=reservoir wiki article history, which documents a 9-year-long low-grade edit war between pro-landuse and pro-water factions. The comment about "considerable confusion" was first added in 2014, and has stuck, despite several attempts over the years to remove it. This ends our tale. Is it time to more directly recommend that mappers favor natural=water + water=reservoir *instead of* rather than *in addition to* landuse=reservoir? [1] https://wiki.openstreetmap.org/wiki/Proposed_features/Water_details [2] https://taginfo.openstreetmap.org/tags/?key=landuse&value=reservoir#chronology [3] https://taginfo.openstreetmap.org/tags/?key=water&value=reservoir#chronology
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