A quick definition of a qua:

Aqua: A Latin word that means water. In Roman law, it can also refer to a watercourse or flowing water. There are different types of aqua, such as fresh water (aqua dulcis), salt water (aqua salsa), and spring water (aqua fontanea). Aqua can also be used in servitudes, which are legal rights to use someone else's water source or discharge wastewater on their property.