When you get an Atma, you'll know it, even without looking in your inventory. In this video, you'll see the drop happen around 10 seconds and then at 14 seconds, a nice big sign to the right of my character and a distinctive sound to tell me "Hey, you got the drop!". The notification lasts for about 4 seconds, so you won't miss it. Best of luck. That was my 4th Atma of the Waterbearer.