In severe cases, the viral infection causes a high fever, bleeding into the skin, and necrosis (death) of cells in the kidney and liver. The damage done to the liver from the virus results in severe jaundice which yellows the skin. Hence, the yellow in yellow fever..
filter definition: The definition of a filter is something that separates solids from liquids, or eliminates impurities, or allows only certain things to pass through. (noun) A Brita that you attach to your water faucet to remove impurities from you...
There are just as many water filters as water softeners. A carbon filter is a type of filter that will remove the most contaminants by itself. These filters are capable removing or reducing hundreds of contaminants in the water. A water softener is not something you need, however a water filter is always a good idea.