The purpose of the hot water bag is to alleviate certain symptoms and/or dysfunctions generated by illnesses on the human body, such as: muscle pain and contractures, lumbar sciatica, back pain, menstrual pain, stomach cramps and pain of rheumatic origin. Heat generates an increased blood flow to the targeted area, which induces a reduction in the contraction of the affected organ or area, exerting an analgesic effect and muscle relaxation. It should never be used, however, if there is acute inflammation, trauma or an infection in progress: in fact, it would increase blood flow, worsening swelling and pain. The liquid to be used inside can only be drinking water at an appropriate temperature.