Fresh water is essential to our health and comfort. Not only do we rely on it to stay hydrated, we use it in many other ways including bathing, cleaning and cooking food, and laundering our clothes. Fresh water has long been a concern of both public communities and private individuals, and several different water purification systems and treatment technologies have been developed to help ensure that tap water is safe for human consumption. But how do these different technologies compare?

Whether you get your water from a well or a city system, water sources can become contaminated by bacteria, runoff, and improper treatment. Even if water isn't contaminated, it may contain iron and other hard minerals that cause discoloration and can build up in the body, or chlorine that leaves an unpleasant odor and taste. Consequently, many people choose to treat or filter their water to improve flavor and protect against contaminants.

Chlorine is commonly used by municipal water treatment plants and is effective in killing many different bacteria. However, it is not effective against some organisms such as Cryposporidium and Giardia. Both of these organisms can be found in lakes, rivers, and ground water and can cause serious intestinal illness.

As mentioned, many people feel that chlorine leaves an unpleasant taste and smell. In addition, there have been numerous cases where the city water supply became contaminated despite the fact that it was treated. People with city water supplies often use other water purifiers and home water filters to ensure that their water is pure and tastes good. The three most common options are carbon filters, reverse osmosis water filters, and ultraviolet light water purification.

Each of these technologies uses a different approach to treat water, and they each have different levels of effectiveness against various contaminants. One may work well to remove chemicals but be completely ineffective against bacteria, and vice versa.

In reality, there is no single filter or treatment that will eliminate every contaminant from your water. The best approach is to have your water tested for contaminants and then purchase a home water purifier that guards against the particular contaminants that cause you concern.

Another option is to combine treatment technologies. Most higher-end systems use a combination of carbon filters and one of the other treatment technologies to achieve the best results. Let's look at the different technologies to see where each is effective.

Carbon Filters
Carbon is one of the most powerful absorbents available and it has been used for many years as a means of removing impurities. The absorbing powers of carbon can be further enhanced by adding a slightly positive electrical charge. This is known as activated carbon, and it is used in many standard home water filters. As the water passes over the positively charged carbon, the negative ions of the contaminants are drawn to the surface of the carbon granules and removed from the water.

Activated carbon filters typically use granular activated carbon (GAC) or powdered block carbon. Both work well for filtering and purifying but carbon block filters have been shown to remove more contaminants. Either type of activated carbon filters help reduce or remove a wide variety of contaminants, including:

• volatile organic chemicals (VOCs)
• pesticides and herbicides
• chlorine, radon, and other chemicals often found in tap water.

All of this protection comes in a relatively inexpensive package. You can purchase carbon filter systems that fit on your faucet for about $30, or you can choose a whole house water purification system that utilizes carbon filter technology for around $100.

However, unless they are densely compacted, most carbon block filters are not effective at removing heavy metals or bacteria. For this reason, many people consider combining carbon filters with one of the other types of water purification systems.

Reverse Osmosis Water Filters

Reverse osmosis, also known as hyperfiltration or ultra-filtration, was developed with U.S. government funding as a means of desalinating ocean water. A reverse osmosis water purifier uses a semi-permeable membrane that allows pure water to pass through it, while contaminants are trapped by the tiny pores in the membrane.

The process requires that the water be pressurized to help force it through the membrane. Most standard residential water systems have sufficient pressure. Like activated carbon filters, reverse osmosis also uses charged particles to help filter out impurities.

The effectiveness of a reverse osmosis water purifier depends on the density of the membrane. A membrane with larger pores will obviously let larger impurities pass through. It is also important that the membrane be cleaned regularly for proper functioning.

Higher quality reverse osmosis water filters use a process known as crossflow to allow the membrane to continually clean itself. Crossflow directs some of the water downstream from the membrane, sweeping the rejected contaminants away so they do not build up and block the membrane.

There are two types of membranes commonly used in reverse osmosis water filters --Thin Film Composite (TFC) and Cellulose Triacetate (CTA). TFC membranes are noticeably more effective the CTA membranes but they tend to be less resistant to the deteriorating effects of chlorine. This problem can be avoided by using an activated carbon pre-filter to remove the chlorine first.

Reverse osmosis water purifiers come in different sizes and styles including countertop and whole house water purification systems. They are capable of filtering out a long list of contaminants including:

• chlorine and other treatment related products
• bacteria
• salts, sugars, proteins
• dyes
• heavy metals

One drawback of reverse osmosis water filters is that they are more expensive than carbon filter treatment systems, with the average home system costing around $300. Also, the purification process is usually somewhat slow due to the use of pressurized water. It can take an entire day to produce 15 gallons of purified water. And a typical reverse osmosis water purifier may need up to 8 gallons of untreated water to generate a single gallon of purified water.

UV Water Purification

As the name implies, ultraviolet light water purification systems use ultraviolet (UV) light to treat water and render microorganisms harmless. The UV light comes from a high intensity lamp that is usually enclosed in a protective quartz sleeve. When water passes through the water treatment system, the UV light damages the structure of any organisms and makes them sterile.

Although a UV water purifier requires electricity to operate, it draws about the same amount of energy as a light bulb. However, the lamp bulb itself needs to be replaced every year to ensure adequate intensity.

While whole house UV water purification systems are effective on most bacteria, viruses, molds, algae and other organisms, they do not remove chlorine, heavy metals, VOCs, or other chemicals. And countertop UV systems, which expose the water to UV lighting for less time, do not always remove all organisms.

UV water purifiers average around $700 for a whole house system, making them more expensive initially than other types of treatments. In addition, without a pre-filter system, contaminants can build up and reduce the intensity of the UV lamp. For these reasons, many people combine UV water purification systems with carbon filters, which also increases the costs.

As you can see, each of the three common water treatment technologies has its advantages and drawbacks. Deciding which is best depends on your budget and the type of water contaminants you want to remove or prevent. A test of your tap water will help you determine the appropriate water filtration system for your needs.