Why is my light on? On the left hand corner

So I went out to a friend just fixing my bike suddenly it started to rain really bad my phone was in my pocket I was trying to get home asap then I gave my phone a few wipes and I look at the top left corner and the light it on so i'm wondering what happened and the phone started making weird noises and I opened the back cover I see water I got mad because the phone wouldn't turn on and all you see is water on the screen and my question is Did the light turn on because of the water or something else I need to know