Which term refers to a method of water purification using passive diffusion?

The term that refers to a method of water purification using passive diffusion is osmosis. Osmosis is a natural process in which water molecules move from an area of lower solute concentration to an area of higher solute concentration through a semi-permeable membrane. This process allows for the removal of impurities and contaminants, as the purifying action relies on the differential movement of water rather than requiring any external energy or mechanical force.

In addition to osmosis, other methods mentioned such as filtration, evaporation, and distillation function differently. Filtration typically uses a physical barrier to separate solids from liquids but does not involve passive diffusion. Evaporation involves changing water into vapor, which can leave impurities behind but is a different process from diffusion. Distillation employs boiling and condensation to separate substances based on their boiling points, also not directly involving diffusion mechanisms. Thus, osmosis stands out as the process that utilizes passive diffusion specifically for the purpose of purification.