All You need is Barrel(Water), Barrel (Empty), Button and health granter
First set the buttons Title to Drink and make it invisible when game starts and put in (When button pressed, transmit on) to say Drink Water
The click on Barrel (Water) and set it to disappear when receiving Drink water
Then Click on Barrel (Empty) and set it to be invisible at game start then have it set to appear when receiving Drink Water
Then go to the health granter and set it to only grant shield and set it to grant however much you want and have to grant it upon receiving Drink Water
Your finished product should look like this!