iPhone touch screen unresponsive when at low battery?

3 weeks ago I fell into a river and my iPhone was in my pocket. I immediately pulled it out, it wouldn't turn on/was dead. I tried the rice trick, and after 48 hours phone works fine although touch screen does not work on small spots.

Today however, the touch screen would be unresponsive for first few seconds after turning on phone, then would be perfectly fine afterwards although slightly sluggish. As the battery goes down through the course of the day this period of unresponsiveness gets longer and longer, until at 50% the touch screen is completely unresponsive, no matter how long I wait/swipe. Is this a hardware issue? If it is, is it fixable/worth to fix?