Rain water is frequently contaminated by impurities taken up from the surfaces on which it falls. Such
impurities include decayed leaves, soot, feathers, etc. Lead and zinc may also be dissolved if the water passes
along pipes or is collected from galvanized roofs. The only circumstances under which rain water can be
used with safety without being filtered are in the open country where the atmosphere is free from impurities,
and where clean vessels are used to collect the water.
