Water systems in ancient times used gravity to move water. They used pipes or channels usually made of clay, lead, bamboo or stone. Today, water-supply systems use a network of high-pressure pumps, and pipes are now made of copper, brass, plastic, or other nontoxic material. Drain and vent lines are made of plastic, steel, cast-iron, and lead. Lead is not used in pipes today because it can be poisonous.