SciTech

How Things Work

Water treatment plants use a series of filtration steps in removing unwanted dirt and contaminants to make water healthy and drinkable.  (credit: Courtesy of Wikimedia Commons) Water treatment plants use a series of filtration steps in removing unwanted dirt and contaminants to make water healthy and drinkable. (credit: Courtesy of Wikimedia Commons)

Water for drinking is a necessity typically associated with high standards. As such, we adopt measures to ensure we drink the kind of water we want. Some people feel safe and comfortable drinking water straight from the tap; others choose to only drink bottled or filtered water. Is one method better than the other?

In the United States, the Environmental Protection Agency (EPA) has set up certain standards for drinking water that ensure that tap water will be “safe to drink for healthy people,” according to the EPA publication “Filtration Facts.” These standards are among the highest in the world, and they set levels for contaminants that can be found in water; the maximum levels are low enough that they will not harm healthy people.

Generally, to meet these standards, water treatment plants follow a series of processes to filter water. Water is first extracted from either above or below ground; water coming from underground tends to be cleaner because it has been sheltered from many pollutants. Extracted water then goes through the process of coagulation: Alum, iron salts, or organic materials are added to the water, and the mixture is left to settle. The added particles attract dirt and other impurities to form big sticky particles called “floc,” which slowly settle.

The water left on top is then filtered, passing through layers of increasingly fine filters made of materials such as sand, stone, and charcoal. Finally, chlorine and other chemicals are added to the water to disinfect it and kill off any harmful microorganisms. The treated water can then be sent off to individual consumers who use it in various ways.

Such filtering and treatment processes usually make water clean enough to meet everyday needs. Still, many people prefer to further filter water in their own homes for several reasons.

The Water Resources Research Center, a research group at the University of Arizona that studies water policy issues, outlines a few reasons why people reject tap water. At-risk groups such as pregnant women and people with fragile immune systems prefer alternatives to plain tap water because their special health requirements make it necessary for them to only drink very pure water. Some at-risk groups say they don’t like the taste of tap water, and others suspect their tap water is not as pure as it should be.

There are several reasons people might not receive water that meets EPA or other cleanliness standards. Pipes that supply water to homes can be old and can leak impurities, and some water treatment plants might not meet the necessary standards for water quality. Consumers can check this by asking their local plant for a report on water quality. They can also access an online database, such as the one created and maintained by the Environmental Working Group (EWG) that analyzes the quality of water in different communities. The EWG is a nonprofit that collects data related to health issues and makes them more accessible to the public.

Research conducted by the EWG shows that there are 300 contaminants present in drinking water for which the government has set no limits. In addition, the water supply for around 50 million Americans doesn’t meet the standards set by the EPA because of an excess of at least one pollutant. Statistics like these could be the reason for the growing popularity of home filtration systems.

More than 40 percent of Americans now use a personal water filtration system, according to the EPA. Home filtration systems come in several types and use many different methods. Most of the cheapest systems available are carbon filters. The carbon in these filters traps most contaminants and only lets water and minute impurities through. One of the downsides of using these systems is the users need to make sure they replace the carbon filter regularly to ensure maximum effectiveness.

For those looking to remove almost every contaminant from their water, a reverse-osmosis unit is effective. These units tend to be more expensive, costing around $100, but they do a more complete job of cleaning water by passing it through a semi-permeable membrane using very high pressure. Ultraviolet light is also used in some water filters to kill any microorganisms that might be present, but this UV light cannot remove chemical or physical contaminants. Combinations of reverse-osmosis and other technologies are available for people who wish to extensively filter their tap water.