The Environmental Protection Agency (EPA) has recently released information stating that, no matter where we live in the United States, there is likely to be some toxic substance in our groundwater. Indeed, the agency estimates that one in
five Americans, supplied by one-quarter of the nation’s drinking water systems, consume tap water that violates EPA safety standards under the Clean Water Act.

The most obvious solution to water pollution is a point-of-use water
purification device. The tap is the end of the road for water consumed by our families, so this is the logical, and most efficient, place to focus water treatment.

• Different water purification technologies each have strengths and weaknesses, and are particularly effective against specific kinds of
  impurities or toxins.
  
• Reverse osmosis and activated carbon filtration are complimentary processes.
  Combining them results in the most effective treatment against the broadest range of water impurities and contaminants.
  
• Reverse osmosis (RO) is a water purification technology that utilizes normal household water pressure to force water through a selective semi-permeable membrane that separates contaminants from the water. Treated water emerges
  from the other side of the membrane, and the accumulated impurities left behind are washed away. Eventually sediments builds up along the membrane and it needs to be replaced.
  
• Reverse osmosis is highly effective in removing several impurities from
  water: Total dissolved solids (TDS), turbidity, asbestos, lead and other heavy metals, radium, and many dissolved organics.
  
• RO is less effective against other substances. The process will remove some pesticides (chlorinated ones and organophosphates, but not others), and most heavier-weight VOCs.
  
• However, RO is not effective at removing lighter-weight VOCs, such as THMs (the chlorine by-product) and TCE (trichloroethylene),and
  certain pesticides. These compounds are either too small, too light, or of the wrong chemical structure to be screened out by an RO membrane.

Note: RO systems have two major drawbacks.

• First, they waste a large amount of water. They’ll use anywhere from 3 to 9 gallons of water per gallon of purified water produced. This could be a problem in areas where
  conservation is a concern, and it may be slightly expensive if you’re paying for municipal water. On the other hand, this wastewater can be recovered or redirected for purposes other than drinking, such as watering the garden, washing the car, etc.
• Second, reverse osmosis treats water slowly: It takes about 3 to 4 hours for a residential RO unit to produce one gallon of purified water. Treated water can be removed and stored for later use.