The term �water filter� can be a bit misleading, because there are drastically different types of equipment for filtering water that share the same name. Pitchers and faucet mounts filter tap water for drinking, while whole-house water filters reduce contaminants like sediment and rust in your plumbing. The type of water filter that you need depends on the type of contaminants in your water and how much water you want to purify. But its very, very important to test your water before you purchase a water filter. The contaminants in your water will determine the water filter system that�s best for you. If you have more than one of the four classes of contaminants in your water, combine the appropriate water filter systems to remove them. Look for water filters that list NSF or other laboratory certification for the contaminants you need to remove.
There is no such thing in nature as "pure" water. Nearly all water contains contaminants, even in the absence of nearby pollution-causing activities. Many dissolved minerals, organic carbon compounds, and microbes find their way into your drinking water as water comes into contact with air and soil. When pollutant and contaminant levels in drinking water are excessively high, they may affect certain household routines and/or be detrimental to human health.
Obvious problems, such as staining of plumbing fixtures and laundry, as well as many objectionable tastes and odors, may be evidence of excessive levels of contaminants in your water supply. Many of these impurities are naturally present and are considered a nuisance, presenting no hazard to human health. In addition, high nitrate levels indicate contamination by surface water or seepage which may convey other harmful contaminants, such as pesticides, into household water supplies.
Now what to test for:
It's important that you not only know how to test, but that you know what you are testing for and why. Buy a good test kit and you can test for chlorine, ammonia, nitrites and nitrates, pH and water hardness. Every test kit is different, but they all come with written instructions for how to perform the tests. Chlorine kills not only germs, but also your fish. When adding new water to a tank, you need to check your chlorine level with a chlorine test kit. Next, test for Ammonia. Ammonia is the direct result of fish peeing in the water. Ammonia levels inevitably rise if you have fish in the tank. Nitrites
Nitrates are a result of the conversion process of ammonia and nitrite. While not as toxic as either, they should not be allowed to build up.
Testing pH Some fish have no problem with the pH balance of the water, but many tropical varieties do. It is easy to test. Between a measured pH of 6 and 8 is where most fish are comfortable, but a pH of 7 is neutral and safest. Above 8, the water is too alkaline. Below 6, the water is too acidic. Chemicals to correct pH can be purchased at a fish store, but follow label directions very carefully. Though different fish like different pH levels, all fish react badly to sudden drastic pH changes. Try not to change the pH more than a point or two in 24 hours.
Water hardness testing is not especially critical, but should be done on occasion to prevent a shift in water quality over time.
Bottom line is, its very important to test your water before buying water filters.