A O Smith MT-4 is a water purifier that uses a three-stage filtration process to remove impurities from water. The first stage, the particle filter, removes suspended solids, rust, sand, silt, organic matter, and prevents crystallization of calcium and magnesium ions in the filtration system. The second stage, the carbon filter, removes odors, chlorine, chloramine, and improves taste. The third stage, the reverse osmosis (RO) membrane filter, removes viruses, bacteria, trace metals, heavy metal ions, and pesticide residue.

The A O Smith MT-4 is easy to install and maintain. The filter replacement cycles are based on statistics of international average indicator, but local water quality and water consumption will affect the lifespan of each filter. The system is designed for ordinary household water consumption and is not intended for use in public places of high or commercial water consumption.