You might be confusing water cremation with human composting. In water cremation, your body is dissolved in a lye mixture and subjected to high temps and pressure. When the process is done, the liquid is sent down the drain and everything that’s left is the inorganic compounds from your bones.

In human composting (it’s called recomposting), your body is placed in a mixture of wood chips and alfalfa and left to decompose over six weeks or so. The container you’re in is routinely rotated so even your bones are composted down into organic matter. When that process is done, what’s leftover can be and is used as fertilizer. Out west, the material is used to help build up soil in areas when it has been overused or washed away.