A hot water bottle is a container filled with hot water and sealed with a stopper, used to provide warmth, typically whilst in bed, but also for the application of heat to a specific part of the body.
While generally used for keeping warm, conventional hot water bottles can be used to some effect for the local application of heat as a medical treatment, for example for pain relief; but here also, newer items such as purpose-designed heating pads are now often used.
Hot water bottles continue to remain as a popular in Ireland and the United Kingdom, developing countries and rural areas. For example, it is widely used in Chile, where it is called a “guatero”. There has been a recent surge in popularity in Japan where it is seen as an ecologically friendly and thrifty way to keep warm.
Some newer products function like the older bottles, but use a polymer gel or wax in a heat pad. The pads can be heated in a microwave oven, and they are marketed as safer than liquid-filled bottles or electrically-heated devices.
Hot water bottles are meant to contain very hot fluids and also supposed to be in contact with human skin. This is therefore of utmost importance to ensure, mainly through standards and regulations, that the closing and welding is stable enough to prevent burns, but also to make sure that the bottle’s chemical components are not dangerous for human health. More generally, it is crucial to certify and assure that hot water bottles, whether manufactured, sold or imported are safe.
For instance, the United Kingdom defined British Standards on hot water bottles to regulate their manufacturing and retail as well as ensure their compliance with all safety standards. The British Standards BS 1970 and BS 1970:2012 (updated version) define, for instance, the bottles’ filling characteristics, safety instructions, allowed materials and components as well as testing methods such as tensile tests for PVC bottles.
Most regulations applied to a country are generally harmonized in order to be applied and applicable in a larger area, such as a trade zone.
Boiling water is not recommended for use in hot water bottles. This is due to risks of the rubber being degraded from high-temperature water, and the risk of injury in case of breakage. One manufacturer (which complies with the British Standards) recommends using water no hotter than 42°C (107.6°F). Other manufacturers suggest a range of safety do’s and do not’s including regular inspection of hot water bottles to ensure that there are no signs of deterioration and safe limits on how far you can fill a hot water bottle – typically 75% is the suggested limit.