Foul water drainage is the system of pipework that carries wastewater away from bathrooms, kitchens, and utility rooms. Foul water is contaminated with pollutants, such as human waste and harmful chemicals, and is directed through the main sewer system to a sewage treatment plant. Foul water drainage is separate from surface water drainage, which carries away rainwater from gutters, patios, driveways, roads, and sports fields. Surface water is not contaminated and is transported to a stream, river, or soakaway. It is important to keep the two water drainage systems separate to ensure the health and safety of the water system. If foul water is directed into surface water drains, any local watercourse that it then discharges into will be polluted with the contaminated water. Conversely, when excess surface water enters foul water drains, the system can become overwhelmed. Therefore, it is essential to ensure that foul and surface water are kept apart in completely separate drainage systems.