White Horizontal Lines On Black Screen

Hello,

A friend of mine, definitely not me, dropped their iPhone 4s down the pan. It apparently took a slight knock on it's journey into the abyss before being falling victim to the flush of water.

It's hunger for life was all gone after this ordeal so I replaced the battery and now I can hear notifications coming through from messages and the 8:00AM alarm is keeps going off.

The question being, does anyone know of a possible cause/fix for the horizontal white lines on a black screen? This display slightly hinders my ability to play apps to their full potential, but I still carry it around and take it out in public/when talking to someone so that they know I'm not a loser who doesn't have an iPhone.

Helpful answers will be repayed in keks.