I'm finding if I don't have enough water for an attack that the buttons don't appear.
Sometimes I have to refresh the page about 3 times or so to get the button to appear under an avatar I am trying to help. (Or there seems to be a cool down period of a few minutes between hits).
You will only see the buttons under the opposite team members.
Edit: I was just able to give Gremmie some water ( you must have it on Lady Pengwings team).