we build a waterproof drone that takes off and lands in water. the motors are fine to get wet, most ESC's are wrapped in shrink wrap and you can spray any exposed wires o CAP's with different types of chemicals that will make them waterproof.
You have to be a little more clever when it comes to the flight controller, Rx, video Tx etc to be able to ventilate the heat and you can't make it a completely watertight compartment because of the barometer. You have to have a way to equalize the air pressure or it won't hold altitude.
This is a fun example of waterproofing drones: