Osmosis is the process in which solvent is transported down the concentration gradient across the cell membrane. Osmosis is the passive transport which do not require any use of energy to transport the molecules across the cell membrane.
Water molecule is transported by facilitated diffusion in which specialized water channels are used to facilitate the transport of water across the cell membrane through osmosis.
These specialized channels are called aquaporins which are present in both plant and animal cell membrane to pass water across the membrane.
So, water crosses the plasma membrane primarily by means of osmosis.
