Water inside phone screen

You probably shouldn’t. An iPhone with water inside is a potential fire hazard. Take it to an Apple Store or Apple Authorized Service Provider (AASP) for further examination:

• Genius Bar Reservations: Genius Bar Reservation and Apple Support Options
• Locate Apple Stores & AASP’s: Find a Reseller 
• iPhone Service & Repair: iPhone Repair & Service - Apple Support

Have a wonderful day and good luck!

Water and other liquid damage to iPhone or iPod isn't covered by warranty. Service for liquid damage to an iPhone or iPod isn't covered by the Apple One-Year Limited Warranty.

Water and other liquid damage to iPhone or iPod isn't covered ...

trixiedinosaure wrote:

Will the water trapped inside go away on its own?

It may dry out eventually. After that, the conductive matter left behind will be your next concern.

and what would happen if I didnt take it to immediate care?

As the water is sitting there, it’s corroding the guts of your iPhone. This may cause shorts in the electronics of the device, causing further damage and creating a potential fire hazard.

I would strongly suggest you don't. (Especially because it is an older phone.) I would take it to apple, they can transfer the data from your existing iPhone to a new one and give you a discount on a new iPhone if you trade in. (I highly suggest the iPhone 13)