Your first step should be to contact your water utility company and request for your water to be tested for impurities, or ask for a copy of their Water Quality Report. The test results will tell you the type of contaminants that are found in your water. This will also give you a guide as to what filtration system for water would be appropriate for your needs.
Then, determine whether what you prefer is a faucet-mounted system or an in-line system. The faucet-mounted system is cheaper and easier to install but needs frequent changes of water filters. The in-line system can be mounted directly to your plumbing. While it is more expensive than the first option, it is more comprehensive and filter changes are done only on occasional basis. The latter is a better filtration system for water if your water test results show sodium, nitrate, ferrous iron, lead and other organic contaminants.
Besides the above two systems, you can also opt for a whole house filtration system for water, or a point of entry unit that clean water as it runs and remove the impurities before it even reach your under sink pipes. It is also possible to install the combination of the two. You select the system containing the water filter that is effective in removing the type of contaminants in your water. A carbon water filter, for example, removes chlorine and heavy metals. It is important that you choose the system that is NSF certified to remove the different kinds of impurities.
Different water filters use varying methods of removing contaminants from your water. Various elements can be used as a piece of filtering products within the system. Carbon filter has been mentioned above. The other element used in filtering water is the granulated charcoal. It works by catching and trapping the contaminants as the water flows. However, this filter has not become popular, because contaminants that are small enough can pass through it with the water. In the recent years, chemical processes have been added to the water filtration system. The chemicals can literally separate the contaminants from the water by attracting them by means of charges.
If you have chosen the filtration system for water that you would like to install in your household, you should first research about its maintenance. Because some of these systems require that filters should be changed after several months; others need the services of a certified professional!