A magaqua (被水の勾玉) is an Elona+ exclusive item which can be used to keep you in WET status all of the time except in certain places in South Tyris and Lost Irva.
A typical usage of this item is to help you gain extra speed bonus from Swimming skill and reduce damage from fire, but at the same time it is possible to cause you double damage in case of lightning. (in recent versions of E+ cold damage is also amplified by being wet).
While a maqaqua is in your inventory, swimming will not be trained.