Saara, after noticing that, used more Spiritual energy. At this time, more water went toward Oliver. But Oliver also wasn't slow because he also used his full spiritual energy to charge the flame stone. So, that flame stone also releases full flame and tries to vaporize the water. That flame also created a layer around him and prevented the water from reaching him.
Sometime later,
Inside of that water prison, you can see that the flame layer that Oliver created to protect himself from the water and also to vaporize the water, decreases in power. Well, it was natural because the spiritual energy of Oliver was very low compared to Saara's. So it was natural that Oliver would feel exhausted after trying to maintain the flame layer around him. But it doesn't mean that he gave up. He was just searching for a chance to break through from this prison and attack Saara.
