What is the primary purpose of a life jacket?

The primary purpose of a life jacket is to keep a person afloat and significantly reduce the risk of drowning. Life jackets are designed with buoyant materials that ensure the wearer remains on the surface of the water, thereby allowing them to breathe without the need to swim or tread water. This crucial feature provides individuals with a better chance of survival in emergency situations, particularly in rough seas or unexpected water incidents.

While other options might have some merit in specific contexts, they do not represent the main function of a life jacket. For example, while life jackets can provide some warmth when in cold water (the first option), their fundamental design and intent is focused on buoyancy and floatation. The collection of rainwater for drinking or serving as a signaling device might be peripheral benefits in certain scenarios, but these are not the primary reasons for their use. Ultimately, life jackets are essential safety devices aimed at preventing drowning, which is why the correct answer emphasizes their role in flotation.