By doing that, she was just following the advice of her Divine Mage System.
Steven, as for him, just nodded, he certainly wasn't going to refuse to take advantage of this water.
It would allow him to train much longer without feeling the effects of fatigue, and as Cassy had just said, it was best to always keep some in his storage ring in case something unexpected happened.
Also, even though he could easily get credits from killing magical beasts with Adrian in the forest surrounding the Academy of Catara, level 3 magic pills weren't cheap anymore, so by using her water from her Divine Space, it would help him save some credits and he could use them for other things.
As he took out 10 bottles of water and with Cassy's help filled them with water from her lake she curiously asked him, "Steven, just now I tried to absorb the spiritual energy and send it directly to my red flame like you told me to, but I couldn't, it's like there's a blockage, do you know why?"