Ma'anar ƙamus na kalmar "ma'aunin ruwa" yana nufin ma'aunin ma'auni da ake amfani da shi don auna yawan ruwa. Yawanci ana bayyana shi a cikin raka'a kamar lita, milliliters, ozaji na ruwa, galan, ko pint. Ana amfani da ma'aunin don tantance adadin abin ruwa a cikin akwati, kamar kofi ko kwalba. Ma'aunin ruwa ya bambanta da bushewar ma'aunin, wanda ake amfani da shi don auna yawan busassun abubuwa kamar hatsi ko foda.