Purified water is suitable for many applications, including autoclaves, hand-pieces, laboratory testing, laser cutting, and automotive use. Purification removes contaminants that may interfere with processes, or leave residues on evaporation. Although water is generally considered to be a good electrical conductor—for example, domestic electrical systems are considered particularly hazardous to people if they may be in contact with wet surfaces—"pure" water is a poor conductor. The conductivity of sea-water is typically 5 S/m, drinking water is typically in the range of 5-50 mS/m, while highly purified water can be as low as 5.5 μS/m (0.055 μS/cm), a ratio of about 1,000,000:1,000:1.