Activated Carbon filters are among the most common home water treatment systems for problem water because of their effectiveness, ease of use and cost efficiency. They are most often used to eliminate undesirable odors and tastes, organic compounds and residual chlorine. They also can remove some potentially hazardous contaminants such as radon gas, herbicides, pesticides and trihalomethanes. Additionally, activated carbon in specially designed precoat and solid block filters is effective in reducing some heavy metals such as lead from drinking water.