Various embodiments of a toilet fill valve lock and method for adjusting the fill water level in a toilet are provided. In one embodiment a toilet fill valve includes a riser that extends along an axis and an inner shaft that is disposed along the axis between the axis and the riser. The toilet fill valve further includes a lock that is moveable toward and away from the axis and which can limit the movement of the riser relative to the inner shaft about the axis when in a locked position.