Interesting question, thanks katier! I think there’s two parts to this answer. The first bit is that quite a lot of the water is contained in the cells of your body. For example, if you took a hundred water balloons and filled them all with water, you’d have a lot of water but you wouldn’t be able to direct see or feel it, because it’s contained in something else.
Water is also contained in other types of fluid. Your blood plasma, for example, is mostly water. There’s fluid in your eyeballs, spine, and surrounding your brain as well, which is all made up mostly of water! And your mouth is always lubricated, which you can both see and feel!