Theretically, you can heat up any liquid with it, but it has a heating coil and a motor that stirs the water. I can't tell you what the long-term effects on hygiene are, but the device is intended for something else, namely for heating up a water basin for a long time. If you want to use it to heat up soups or keep them warm, you would probably just have to put the soup in another container in the water basin so that it takes longer to heat up but you don't have a problem keeping it warm.