What is the human body made of? The Big Science Question: Depending on who you ask, our bodies are mostly made of water, oxygen or empty space (or £96,000 worth of precious metals and elements, if you are Benedict Cumberbatch) The human body is made up of trillions of cells. Importantly, all of these cells contain a lot of water, meaning that humans are in fact around 65 per cent water. The water in cells helps with chemical reactions, transports oxygen and waste, and acts as a shock absorber. But humans are also not entirely, well, human. Some of these cells are our own, and form our organs, muscles and bones, but a surprising number of them are bacteria.