How to waterproof iPhone 6?

I was wondering if there was a way to make my iPhone 6 more water resistant (like the iPhone 6S). I would consider myself advanced at repairs in general and intermediate with smaller devices such as iPhones/iPads. I'm looking for a product that would be ok internally and would help + if it would be acceptable for the internal parts.

I would also like to know where the most water damage comes from and where it seeps through the phone, any information is helpful!

Thanks!