Water-Based Markers use water-soluble inks. They are generally non-toxic, but not necessarily washable. Read instructions carefully. If you must have a washable marker, select one that specifically features washability.
Washable markers use a more limited selection of inks, based on dyes that are less staining and are more easily removed from fabrics and skin. Because the dye selection is so limited, the colors tend to be both less lightfast and less vivid.