Writing instrument including a feeding assembly, a front barrel and an ink cartridge comprising at least a shutting operculum and a neck extension that is detachable from the feeding assembly of the writing instrument, the feeding assembly comprising at least: a writing point, a stem feeder and a hollow core having a cylindrical rearwards projection forming a detachable connection connecting the feeding assembly to the ink cartridge of international standard size and containing water based ink; the cylindrical rearwards projection having a rearmost sharp end suitable for separating the shutting operculum from the neck extension of the ink cartridge; the hollow core forming a traversing canal and having outer attaching means for securing the feeding assembly to the front barrel of the writing instrument; the hollow core having an ink flow regulator, longitudinally disposed between the attaching means and the cylindrical rearwards projection; the stem feeder extending axially inside the traversing canal and extending frontward out of the hollow core and of a ring abutment; the ring abutment being fixedly attached to and around the stem feeder so that the ring abutment rigidly secures the stem feeder to the hollow core; the stem feeder having a rear end that extends axially rearwardly inside the cylindrical rearwards projection so that the water based ink flows from the detachable ink cartridge to the stem feeder via the cylindrical rearwards projection; characterized in that the stem feeder incorporates integrally the writing point and the writing point comprises a tip that forms frontwards stem end of the stem feeder; and in that the stem feeder including the writing point has a surrounding envelope that comprises merged capillary fibers and a resin substrate; at the outmost periphery of the surrounding envelope a surface protective layer being cylindrical shaped and peripherally / longitudinally to surround the stem feeder, except at its rear and front ends. a writing point, a stem feeder and a hollow core having a cylindrical rearwards projection forming a detachable connection connecting the feeding assembly to the ink cartridge of international standard size and containing water based ink; the cylindrical rearwards projection having a rearmost sharp end suitable for separating the shutting operculum from the neck extension of the ink cartridge; the hollow core forming a traversing canal and having outer attaching means for securing the feeding assembly to the front barrel of the writing instrument; the hollow core having an ink flow regulator, longitudinally disposed between the attaching means and the cylindrical rearwards projection; the stem feeder extending axially inside the traversing canal and extending frontward out of the hollow core and of a ring abutment; the ring abutment being fixedly attached to and around the stem feeder so that the ring abutment rigidly secures the stem feeder to the hollow core; the stem feeder having a rear end that extends axially rearwardly inside the cylindrical rearwards projection so that the water based ink flows from the detachable ink cartridge to the stem feeder via the cylindrical rearwards projection; characterized in that the stem feeder incorporates integrally the writing point and the writing point comprises a tip that forms frontwards stem end of the stem feeder; and in that the stem feeder including the writing point has a surrounding envelope that comprises merged capillary fibers and a resin substrate; at the outmost periphery of the surrounding envelope a surface protective layer being cylindrical shaped and peripherally / longitudinally to surround the stem feeder, except at its rear and front ends.