Reverse osmosis water filters are often used to purify bottled water, taking water right out of the tap and running it through a filtration system before selling it to you in those convenient and expensive bottles. You're not limited to purchasing water purified this way; instead, consider installing a filter to clean your water system. These filters run water through a membrane that allows only clean water to pass through; all other contaminants, from germs to chlorine, remain on the other side of the membrane and are flushed from the system. Almost every major contaminant is removed from your water with this method: chlorine and fluoride, arsenic, heavy metals, nitrates and pesticides, iron (you can get too much), sediments, bacteria and viruses, and even bad taste and smell.

Because of its effectiveness at removing contaminants, a reverse osmosis water filter is often called a hyperfiltration system. It works by sending water from your municipal or private supply through a series of small reservoirs in the filter unit, each containing the osmotic membrane. In the reservoir, clean water moves to the clean side of the filter, leaving contaminants behind. Water passes through via osmosis, not water pressure as is more common for other filters. That means that this filtration system is painfully slow. To address this problem, osmotic water systems include a tank where your clean water is deposited, providing a reservoir of drinking water in the amount of about fifteen gallons each day. This water is of bottled water quality, and if you buy bottled water every day, you can imagine how much money this can save you.

A reverse osmosis water filter may have a thin film composite (TFC) or a cellulose triacetate (CTA) membrane, each of which has strengths and weaknesses. The TFC is best by far at contaminant removal, but it is easily damaged if you have a chlorinated water supply going directly into it. For TFC filters, it's a good idea to install an activated carbon filter upstream of the TFC filter. The CTA filter is not as good at removing contaminants, but it is also tougher and will not be so easily damaged. Because a damaged film can ruin your reverse osmosis water filter, choose carefully between these two options.

If you have a problem with biological contaminants, you should consider using not just a reverse osmosis water filter by itself, but also using an ultraviolet filter, as this filter is the most effective by far in removing biological contaminants without otherwise contaminating your water supply. So your perfect reverse osmosis water filter may need to have a total of three filters to be completely effective at cleaning your water: the activated carbon filter (which needs to be changed regularly), the osmosis filter, and the ultraviolet filter (which needs an electrical power outlet). With these three filters in your system, however, you can be assured of a tasty, reliable, and clean water supply for your home and family.

Your last concern with a reverse osmosis water filtration system: the amount of water used in producing your clean water. Each one gallon of clean water requires up to ten gallons of water, the remainder of which is flushed from the system. If this is a problem in your area, make sure that your contaminated water is redirected to your gray water reservoir, where it can be safely used to water your garden.