There is a tricky part here. You dropped it in water, therefore it needs to get cleaned out immediate to prevent corrosion. This can be done with [[Electronics Water Damage|90% isopropyl alcohol]]
There is still a chance the phone may work after cleaning, so don't give up!
If you cleaned the phone and issue still appears to be the same, then you will most likely need to replace the screen. Not sure if you have the exact model you posted but here is a [guide|76867|breakdown for the a J3|lang=fr]
If you're not comfortable in this realm, just take it to a shop and inform them it was dropped in a pool.
Hope this helps