Is filtered water safer than tap water?

Once upon a time, "drinking water" meant "tap water" -- the stuff that comes from a well or, more commonly, a municipal source. It flows equally into homes, offices, hospitals and restaurants without regard for social standing or economic status. Drinking water was free, it was quick, it had no packaging and no manufacturer's instructions. Satisfying one's thirst was as easy as holding a glass under the kitchen tap.

Those days are gone. Drinking water can be tap, bottled, filtered, mineral, purified, sparkling or enriched. Municipal, well, domestic, imported or mountain spring. Free of charge or costlier than gasoline.

The free stuff is the tap water, the (hopefully) clear liquid that, if you live in a developed country, flows magically into your home and out of your taps. At one time, people didn't give much thought to the source of that magic flow. They drank it, cooked with it and showered in it. It was presumed safe.

That presumption has gone the way of the residential landline: It's still out there, but not in the numbers it once was. Deserved or not -- and we'll get to that later -- tap water raises all sorts of alarm bells these days. In the United States alone, people consumed more than 33 billion liters of bottled water in 2007, and more than 40 percent of U.S. homes have some sort of water-treatment system [sources: Discovery, EPA].

So even when they do hold a glass under the kitchen faucet, they're not drinking plain old tap water. They're drinking the filtered version, which can cost anywhere from $20 to a few hundred bucks to produce.

Is it worth it?

In this article, we'll find out. We'll look at safety concerns surrounding tap water and see if they're valid, learn how filtered water is different, and check out some of the potential downsides of home water treatment.

If you're not one of the water-treating 40 percent, you may be wondering -- what's the big problem with tap water?

Safety Concerns with Tap Water

Tap water's bad press is mostly about three issues: the way it looks, the way it tastes and what's in it. The first two are matters of preference; the third is about safety. Many people who filter their tap water are concerned about contamination.

Is it warranted? Not usually, unless the drinker has a severely compromised immune system. In the United States, municipal tap water systems have to meet safety standards, and they're regularly inspected by the government. The water is heavily treated to remove particles, chemicals, bacteria and other contaminants. Typically, chlorine and fluoride are added for disinfection and dental-health benefits, respectively.

Of course, no system is perfect, and on rare occasions contaminants such as pesticides (like atrazine), pathogens (like E. coli, cryptosporidium and giardia), and fuel byproducts (like MTBE and perchlorate) have been found in municipal water supplies. Well water is more likely than city water to be contaminated, because it doesn't go through the same regulated treatment and testing. And any tap-water supply runs the risk of tasting, smelling or looking bad, simply because of added chlorine or region-specific, innocuous particles that are not specifically targeted in the treatment process.

In the rare case of contamination, the less-rare case of baseless fear of contamination, or the somewhat common case of aesthetic shortcomings, there are two typical solutions: bottled water or filtered water.

Bottled water is a controversial option. It has come out in the last decade that some bottled water brands are selling $2 liters that are no more pure or "mountain spring"-like than tap water (see How Bottled Water Works). And for most people with the slightest green-leanings, bottled water's eternal landfill presence and high-carbon-footprint container makes it a guilty pleasure, at best; at worst, a vicious, absurdly overpriced and possibly fraudulent assault on the planet.

Which leaves filtered water. With some smart implementation, it can be a pretty reasonable approach to cleaning up the tap.

What's the Difference Between Filtered Water and Tap Water?

If tap water tastes like chlorine, filtering can fix that. Filtering can clear out many safety concerns like bacteria, heavy metals and pesticides. Some types of filters can do nearly everything. Others are specific to certain contaminants.

The most common types of filters in home treatment systems include:

Activated carbon -- The most common type of filter and a relatively inexpensive option (it's used in most of those countertop pitchers), activated carbon attracts and absorbs particles. Water runs through a filtering screen containing carbon, where contaminants get stuck. It can remove much of the heavy metals, parasites, pesticides, radon and MTBE that may be in the water. This filtering is typically used in point-of-use devices, like under-sink or faucet-mounted units and pitchers.
Aeration -- Typically used at the point of entry, aeration filtering forces water entering the home to pass of high-pressure air jets. If there are fuel byproducts or radon -- contaminants that easily become gases -- in the water, they evaporate. Aeration doesn't remove other contaminants like parasites or mercury.
Cation exchange -- This is a water-softening filtering approach that uses positively charged particles to attract negatively charged particles (ions), such as calcium, magnesium and barium. Water flows through beads of resin, where the positive ions stuck to the beads trade places with the negative ions in the water. Calcium and magnesium aren't really safety concerns, but they can damage a home's pipes. However, barium can be a health concern.
Distillation -- Boiling water is one of the best ways to remove pathogens and heavy metals, and distillation takes this route. Distillers boil water into steam and then condense it back into water, killing bacteria and viruses and pulling contaminants like lead, mercury and arsenic out of solution in the process. It's often used in point-of-entry systems (where the water enters the home) or in countertop devices.
Reverse osmosis -- One of the most effective and costly filtering methods and typically a point-of-use approach, reverse osmosis uses pressure to force water through a semi-permeable membrane, removing practically all contaminants. This type of filtering is recommended for people with compromised immune systems, since it tends to eliminate more pathogens than other methods. The downside is the waste: About 4 gallons (15 liters) get thrown out for every 1 gallon (3.7 liters) of purified water it produces.
UV Disinfection -- UV disinfection destroys parasites, bacteria and viruses with ultraviolet light. It doesn't remove other contaminants like metals or chemicals from water. UV is often found in point-of-use, under-sink systems.

All of these methods can be effective at purifying water, but that's not the end of the story. Water-filtering systems come with their own set of problems.

Safety Concerns with Filtered Water

Setting up a filtering system at home isn't an automatic tap-water fix. It's a potentially good idea that requires certain steps to implement properly. Without those steps, the system can be ineffective or, worse, detrimental.

The first consideration is your specific tap water. Not all water supplies are alike -- far from it. To implement a useful home filtering system, you need to know what you're trying to filter out. A point-of-entry aerator won't be of any use if you're aiming to eliminate bacteria.

It's easy enough to find out what's in your water if you use the city utility system, which provides water-testing results to its customers every year in the required Consumer Confidence Report. If you haven't received one, you can call your water company and request it.

If you get your water from a private well or you want to be sure the water coming out of your faucet is OK (if you've got an old house with lead pipes, for instance), you can do your own testing. The U.S. Environmental Protection Agency or EPA's Safe Drinking Water Hotline can recommend companies in your area.

There are two more issues to be aware of when it comes to filtered water. First, look for an NSF-certified filter so you know it's doing what it claims. The National Sanitation Foundation, or NSF, tests water-safety products and determines whether they meet national and international standards and live up to their claims.

Finally, and this is a big one, make sure you maintain the filter the way the manufacturer recommends, especially in terms of periodic replacement. If a filter gets overly clogged with contaminants and you just keep running water through it, those contaminants can leak into the water, leaving you with more dangerous water than you started with.

As with any precautionary action, it's best to start from a position of knowledge. Especially before investing in a whole-house system, find out what's in your water, what you want to remove, and how best to do it for your particular situation. Smartly implemented, a filtering system can be an effective and cost-efficient water-safety measure.

For more information on filtered water, water safety and related topics, look over the links on the next page.

Lots More Information

Sources

Boyles, Salynn. "Many Tap Water Filters Work Well." WebMD. April 9, 2007.http://www.webmd.com/news/20070409/many-tap-water-filters-work-well
Consumer Guide to Water Filters. NRDC.http://www.nrdc.org/Water/Drinking/gfilters.asp
Different Water Filtration Methods Explained. APEC.http://www.freedrinkingwater.com/water-education/quality-water-filtration-method.htm#Anchor-Ion-47857
Ingham, Barbara. "Tap Water, Bottled Water, Filtered Water: Which to Choose?" University of Wisconsin.http://www.foodsafety.wisc.edu/consumer/fact_sheets/waterbottles.pdf
Water Health Series: Filtration Facts. EPA.http://www.epa.gov/safewater/faq/pdfs/fs_healthseries_filtration.pdf