When your iPhone 7 Plus comes into contact with liquid, it can cause a very complicated form of damage. Most of the liquids we're exposed to in everyday life contain ions that do an excellent job of conducting electricity. When exposed to the electrical components of your device, these ionic conductors cause the circuits to "short". Rice is commonly used to accelerate the evaporation process, but even after the liquid dries these ionic impurities are left behind and can still cause a short later on. However, electrical shorts are the least damaging aspect of the process. The real damage is done with the combination of water, air, and time, which leads to corrosion. Once your device is exposed to the impurities brought on by water, the chemical process of corrosion begins, and the longer that goes unchecked, the chances of the damage being repairable becomes less and less.