Distilling water may be necessary if water is contaminated with biological agents or chemicals. Many people use it in their aquariums at home and it can be found in most antifreeze formulas.
To make distilled water simply take an amount of water and heat it until it is boiling. The steam should be trapped and run through tubing that will cause it to cool down and condense. The water that drips out of the other end is distilled. It is the easiest way to purify water.