Use a home water-quality test kit to determine the amount and nature of impurities present in the water. Alternatively, you can have a water sample tested at a laboratory. You will need to rely on the test results in order to determine the type of water filtration system you will need.
If your budget is limited, consider investing in a faucet-mounted system or an inline filtration system. The former is inexpensive but requires the filter to be changed over short time period. On the other hand, an inline system is costly as compared to a faucet-mounted system but for this system, filter changes need to be made only occasionally.
If the water test results revealed that chlorine, chloroform, pesticides or organic chemicals are the contaminants that need to be filtered, you should use an NSF-certified carbon filter in the filtration system of your choice. However, keep in mind that the carbon fibre found in a carbon filter are not effective against contaminants such as heavy metals, fluoride and chloroform.
If traces of sodium, ferrous iron, nitrates, lead, fluoride or organic contaminants were found in the water, it would be wise to invest in an inline reverse-osmosis filtering system. The problem with an inline reverse-osmosis filtering system is that it wastes more water than it cleans (4 gallons of water would be wasted for each gallon of pure, filtered water). Be sure to use a water softener in tandem with this system if results reveal high calcium count in the water.
To make sure that the filter in a water filtration system is changed at the right time, it would be a good idea to choose a system that has a cut-off meter.