A hot water bottle is a flexible container, typically made of rubber or thermoplastic, designed to hold hot water. It is used for providing warmth and comfort, often placed under blankets or against the body to relieve pain, soothe muscles, or keep warm during cold weather. To use a hot water bottle, one fills it with hot water, ensuring it is not too full to prevent leaks. The bottle is then sealed tightly and can be applied to various areas, such as the back or stomach, for therapeutic benefits. Hot water bottles are a simple and effective way to manage discomfort and promote relaxation.