Osmosis

Victims of kidney disease rely upon artificial kidney machines to remove waste products from their blood. Such machines use a process called dialysis, which is similar to osmosis. The difference is that the dialyzing membrane permits not just water, but also salts and other small molecules dissolved in the blood to pass through. These move out into a surrounding tank of distilled water. The red blood cells are too large to pass through the dialyzing membrane, so they return to the patient's body.