What facilitates the diffusion of water across the cell membrane?

Channel Proteins. Water does not "diffuse" through cell membrane. However, you could have osmotic pressure created by differences in salt concentrations inside and outside of the membrane driving flow of water (or permeation of water) through the membrane.

Sailors while sailing at night uses certain colors of light to communicate.

According to the given condition, the white light appearing directly ahead of someone's direction, indicates that another boat (vessel) is sailing right ahead and communication must be done by blowing horn or by using the red light(left side/port side) or the green light (right side/starboard side). One must give way to avoid collision.