The iPhone being waterproof (resistant) will lead to so much more issues and problems for children, teenagers and adults as they will more often spend time in bathrooms and perhaps even showers using the phone. Addiction rates will most probably go up. iPhones and other phones which are water resistant will also be used more often at water parks, beaches and on adventure trails where water drops will become less of a worry. Apple will deal with more warranty issues as drops and water spills for the phone will increase.
On the better side of things – amazing photos and videos will be taken, more memories will be captured and taking a separate camera for those amazing events will drop significantly. Most people will use their smart phones more often which will increase higher usage for pretty much everything. 
Now the question is how do you plan to use your new iPhone 7 and iPhone 7 Plus!