Carbon filtration systems are the of water filter

Reverse Osmosis
Reverse Osmosis is a technology from the 1950's that was designed to separate the salt from sea water by passing water molecules through a membrane. While Reverse Osmosis seems to be good for making drinkable sea water there are some concerns with using this type of water filter. Beneficial minerals, like calcium and magnesium are stripped from your drinking water during Reverse Osmosis. This is especially bad for growing children.

Reverse Osmosis systems also waste approximately three gallons of water for every one gallon they purify.

Carbon Filters
Carbon filtration systems are the most common type of water filter. Many of the inexpensive pitcher type filters use this technology. The water is passed through specially treated carbon to remove contaminants. Carbon filters seem to do little more than improving the taste and smell of the water that passes through them - by itself carbon filters do not provide adequate filtration to remove the harmful chemicals found in today's drinking water. Another negative aspect of carbon filter is that if you pure hot water through them it will actually cause the carbon to release all the waste that's been trapt from previous uses. 

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  Domestic reverse osmosis system
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  Water Purifier
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  Water Filter
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  Counter Top Water Filter
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  CounterTop Water Filter
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  Sink Water Filter