Carbon Filters vs. Reverse Osmosis vs. Distilled Water

America has one of the best water systems on the planet. Each day, water treatment plants process 44 billion gallons of water for use in our homes, schools, factories, and farms. This water is delivered through over one million miles of piping, most of which was built after the Second World War. This infrastructure is now nearing the end of its lifespan. Its aging water mains and sewage pipes are becoming less reliable and leaks are becoming more common. As a result, waste and pollution have started creeping into the streams, lakes, and rivers you depend upon for drinking water.  As state, local, and federal agencies struggle to replace and repair our aging water systems, many Americans have realized that they need to take extra steps in order to ensure their homes have clean drinking water. The solution is water filters. They’re an increasing common fixture in many homes and provide a clean alternative to tap water. If you’re worried about the state of your tap water, it’s time to consider the different methods you can use to keep it clean. The three most commonly available are carbon filters, reverse osmosis, and distilled water filters – all of which have their pros and their cons.

Tap water isn’t pure. Even the best contains traces of metals, chemicals, and other substances. Here are some of the most common.

Less common contaminants include radium, aluminum, mercury, cadmium, and barium, which are all toxic or hazardous if ingested in large quantities. All of these substances are monitored by the EPA, though some researchers believe that the EPA’s allows more of them into your water supply than is healthy.

Carbon filtration has been used on and off for centuries, ever since the ancient Egyptians discovered that storing water in charcoal improved its taste and kept it fresh. Modern carbon filters are made by heating carbonaceous material, such as coconut shells or coal, to extremely high temperatures in chambers filled with argon or nitrogen. Activated carbon is extremely porous. One ounce has approximately 151,200 square feet of surface area.  Carbon filters eliminate pollutants through adsorption. They attract chemicals at the molecular level, similar to the way a magnet attracts metal shavings. Harmful particles adhere to the carbon’s surface as they pass through the filter, so they more surface area they have, the more effective they are.

Pros
Carbon filters are extremely good at absorbing chlorine, mercury, SOCs, and VOCs, such as benzene, carbon tetrachloride, dioxin, formaldehyde, and chloroform. They are also the only filter that can safely remove pesticides, herbicides, and total trihalomethanes, a group of dangerous chemicals that are formed when chlorine is mixed with water containing organic matter. (Most of the water on Earth contains organic matter.) They’re also moderately effective at removing lead. Carbon filters are inexpensive and generally easy to install. They’re commonly found in pitcher water filters, like Brita, and water bottle filters like the NewAir WAT10W Water Bottle, which is used with freestanding water dispensers.

Cons
Most carbon filters are made from granulated carbon, which has the same consistency to ground coffee. There is some danger that, with repeated use, the water may cut channels through the carbon that would prevent them from effectively filtering it. Carbon filters are also ineffective at removing inorganic solids and heavy metals. They can also become contaminated with bacteria if  they’re not changed approximately every six months.

Reverse osmosis filters force water through a semi-permeable membrane – a thin, pliable sheet that allows some molecules through it but not others. Researchers at UCLA and the University of Florida began using it to filter water in the 1950’s, and it was first used on a large scale until 1977, when the city of Cape Coral, Florida used it to purify drinking water for its inhabitants.

Pros
Reverse osmosis traps 95-99 percent of all dissolved salts, bacteria, and heavy metals in your water supply. It’s especially good at filtering lead, mercury, calcium, iron, and asbestos. It can trap particles as small as 0.001 microns, 100,000 times smaller than the width of a human hair. In additional, it also removes microbial cysts such as Giardia, Cryptosporidium, and Cyclospora, which can cause severe illnesses if ingested.

Cons
Only about 30-50 percent of all the water used by a reverse osmosis filter actually gets transformed into potable drinking water. The rest is used to flush out the membrane and becomes waste. It’s necessary to keep the membrane from becoming clogged, but it’s also extremely wasteful. Reverse osmosis filters also have difficulty removing SOCs, VOCs, and chlorine. In fact, chlorine actually damages the membrane and has to be filtered out beforehand with a carbon filter. The membranes is also vulnerable to sediment and bacteria, which can grow on its surface.

Home osmosis kits are expensive to purchase and difficult to install. An Aquasana OptimH2O filter system costs $170-$250 and, like most systems, you’ll need to hire a plumber to install it.  By contrast, most carbon filters sell for less than $50 and can be set up in a few minutes without any help.

Distilled water is made by heating water until it evaporates, then capturing the steam and condensing it back into liquid in a separate container. Because inorganic materials have a much lower boiling point than water, they don’t boil away with the water vapor, but get left behind, where they can be safely disposed of. There are a number of companies that sell distilled water filters for home use, including H2O Labs, MegaHome, and Aquanui.

Pros
Distilled water is effective at removing arsenic, asbestos, chlorine, lead, mercury, nitrates, pesticides, salts, and SOCs. Boiling the water also kills bacteria and viruses, and produces some of the purest water imaginable. There’s practically nothing in it but H2O.

Cons
The only thing distilled water filters can’t remove are VOCs. They have a lower boiling point than water, so boiling your water won’t remove them. To compensate for this, most distilled water filters have a separate filter to trap and remove VOCs before they can get mixed back in with your drinking water.

Distilled water filters are more expensive to operate and take longer to filter water than either carbon filters or reverse osmosis. They require 3 kilowatts of electricity to filter one gallon of water, at a cost of $0.35. It’s not much, but reverse osmosis filters only cost $0.18 per gallon, and most carbon filters cost nothing at all. They’re gravity fed and don’t require any electricity. Distilling a gallon of water takes approximately 5 hours. A carbon filter takes less than one hour to filter a full gallon and a reverse osmosis filter can fill a 2-4 gallon tank in 2-3 hours.

Distilled water filters also upset your water’s chemistry. Besides removing harmful minerals, distilled water filters also remove necessary minerals like calcium and magnesium, which promote good health. Distilled water also actively absorbs carbon dioxide from the air, which makes it slightly acidic. In order to balance it out and prevent it from harming your soft tissue cells, your body pulls calcium and magnesium from your teeth and bones. Distilled water is harmless in small doses, but anyone drinking distilled water for an extended period of time may begin to suffer from mineral deficiencies and increase their risk of osteoporosis, osteoarthritis, hypothyroidism, coronary artery disease, and high blood pressure.

The bottom line is that no single filter can remove all of the pollutants in your drinking water. Fortunately, because of the precautions taken by government water agencies, no filter has to. A household filter only needs to remove the chemicals, metals, and sediment your local water plant can’t. These vary depending on where you live, but in general, levels of heavy metals and inorganic solids are tightly controlled and are rarely high enough to put you in danger. That’s why, for most households, a simple carbon filter will do a better job cleaning your tap water than either a reverse osmosis or distilled water filter. They’re not only extremely good at removing chlorine, sediment, SOCs, and VOCs, but they’re also cheaper, faster, and more efficient. Reverse osmosis filters are not only expensive to install, but are also extremely wasteful. Less than half the water is uses actually becomes drinking water. The rest goes down the drain. And while distilled water might be pure, it lacks too many of the minerals we require to make it a long-term solution to your water problems. Stick with a carbon filter.