I’ve just finished reading ‘ The Magic of Reality ‘ by Richard Dawkins, in which the author focuses on the wonder of sensing, and understanding the science of, the natural world around us. He starts each chapter by looking at myths surrounding natural phenomenon and explains how scientific understanding has helped to dispel these myths.
Belief systems are often built up around myths. If your personal belief about your relationship with water is based around the idea that you will sink, you need to dispel that myth by looking at it scientifically.
The human body is made up of tissue with a high water content with a similar density to water, some tissues (muscle and bone) have a slightly higher density, some (fat and lung) have a slightly lower density. As long as the overall density of a human body is less than that of water it will float.
Most people can float, that’s a scientific fact and believing it can greatly help you to enjoy being in the water.