Filtering systems improve water taste, reduce chlorine and organic contaminants and trap such biological contaminants as cryptosporidium. But they don't catch viruses and are minimally effective in blocking radioactive pollutants. Reverse osmosis systems do a good job reducing inorganic contaminants and some radioactive materials, but bacteria and viruses may remain in water after treatment. Unless these systems are closely monitored and maintained, water quality can deteriorate. They also waste more water than they produce, using 3 to 10 gallons for every gallon produced.
Distillation shines as the most effective of all single-step water treatment processes.
It removes all organic, inorganic and radioactive contaminants. But distillation alone does not always take out all radioactive material, such as gasoline and petroleum-based solvents.