IS IT POSSIBLE TO GET BACK MY FILES AFTER WATER DAMAGE AND THE PHONE WONT COME ON

Well yes it's possible. There are never any guarantees with water damage, but the most important thing would be that the processor and flash memory are intact because of encryption. Then maybe that the board isn't destroyed beyond repair, although it might be possible to use a donor board. And it's usually not water that damages phones, but impurities in the water, which along with electricity causes certain parts to fail, such as capacitors shorting or resistors opening. Some fixes are actually pretty simple. There can also be corrosion, which will get worse the longer it remains wet and in contact with corrosive substances - especially salt water. The most gruesome thing I've heard of is iPhones damaged by contact with blood.

A reputable place that does data recovery for severely water damaged devices won't charge if they don't get data, and will typically only repair in order to extract that data. That could mean that it's not returned in any shape where it could be indefinitely used. It could require use of temporary donor parts that then comes off after the backup is extracted.

Nobody here can recommend a specific place to do this, but you can search for places that do this near you or that have mail-in service. What happens after that is another story. Apple may or may not accept such a device for its replacement service, but even then I'd recommend getting a newer phone like an iPhone 7 or 8.

The best plan to mitigate such damage is to have a good, regular backup, but unfortunately not everyone is diligent about it.

Apple does not offer data recovery services.

If you were backing it up on a regular basis, just restore the last backup to your replacement phone.

if you have a backup in icloud or on a computer with itunes you can restore it to a new phone

No way to do anything with that destroyed device.