You are correct that microwaves work by heating up water molecules in food. When microwaves pass through food, they excite water molecules, causing them to vibrate rapidly, which generates heat. This heat, in turn, warms up the surrounding food.
While our bodies do contain a significant amount of water, several factors prevent us from being "cooked" by the microwaves in our environment:
Limited exposure time: The exposure time to the low levels of microwave radiation emitted by household appliances is relatively short and sporadic. Microwaves in ovens are designed to be contained within the oven's metal walls, and the microwave door's design prevents significant radiation leakage. Furthermore, the microwave radiation emitted by appliances like cell phones, Wi-Fi routers, and microwave ovens is generally at very low levels and considered safe for human exposure.
Minimal absorption: Human skin is not very efficient at absorbing microwave radiation compared to substances with higher water content, like food. The outer layer of our skin is relatively dry, so it doesn't absorb microwaves effectively.
Lack of penetration: Microwaves have limited penetration capabilities in the human body. They can only penetrate a few centimeters into the body before their energy is significantly absorbed and dissipated as heat. Therefore, they do not reach the internal organs where they could cause significant harm.
Safety regulations: Microwave ovens and other devices that emit microwave radiation are subject to safety regulations and standards. Manufacturers ensure that their products meet safety guidelines and are designed to minimize any potential health risks associated with exposure to microwave radiation.
It's important to follow manufacturer instructions for using microwaves safely and avoid tampering with microwave oven seals or using damaged microwave ovens. Generally, when used correctly, microwave ovens and other microwave-emitting devices are considered safe for everyday use.