Admin actions are explained on this page.
Any report can be hidden by the author or by a moderator. Hidden reports can be unhidden immediately after the action or through the database. No data is lost.
Any water source can be hidden by a moderator. Hidden water sources can be restored, no information is lost.
Some water sources were created by mistake, they can be annihilated forever without leaving a trace. They can not be restored.
It is only possible to annihilate water sources that were created first on Rodnik.today (without a connection to OSM) and have no visible reports. (You can annihilate a water source with hidden reports.)
Usually, there is no need to invalidate and regenerate tiles manually, because it is done automatically. Is something goes wrong, this action gives you an alternative way to fix it. Tiles of all zoom levels containing this water source will be regenerated.