But if your drinking water contains dangerous levels of other pollutants, you’ll need to choose a water-treatment technology that is appropriate for eliminating the toxins. For the sake of discussion, it’s easiest to group toxic pollutants into four categories: organic chemicals, inorganic chemicals, radionuclides, and microbiological organisms.

Organic chemicals include solvents, pesticides, synthetics, resins, and other manmade chemicals known as volatile organic chemicals (VOCs). VOCs are often linked with cancer and/or nervous system, liver, and kidney disorders. A particularly nasty compound, trihalomethane (THM), can be created after water has left a treatment plant and the chlorine reacts with decaying animal and plant matter, creating chloroform, a suspected carcinogen.

Inorganic chemicals include nitrates and nitrites, asbestos, fluoride, and metals such as arsenic, mercury, and—the most notorious—lead. Many of these occur as natural mineral deposits. Some, such as copper and lead, leach into water as it travels through pipes and treatment by your water utility doesn’t remove them.

Why we like it: • Checks for presence of 8contaminants, including hardness and lead • Great way to pre-screen before labtesting • Easy to use

Nitrates and nitrites are produced by industry or farming. Inorganic chemicals are associated with a variety of health problems. Lead is known to cause brain damage and is particularly toxic to infants and pregnant women. Pre-1930s plumbing in some areas utilized lead pipes, and solder used to join copper piping in homes before 1986 has a lead content of about 50 percent.

Radon gas, the most common radionuclide, occurs naturally in a number of regions, including Western mountain states and parts of the Northeast. The EPA estimates that up to 17 million people may have water with excessive levels of radon, which can enter the air through showers and steam.

Microbiological contaminants, including protozoa, bacteria, and viruses, are normally killed by chlorination and treatment. Cysts, such as cryptosporidium and giardia, are more resistant to municipal treatment. Normally, bacterial pollution problems occur only when water treatment breaks down, or if a home’s water supply is tainted by waste. Cyst problems tend to occur during times of heavy storm runoff.