Humans require access to abundant, clean water to sustain health. Water quality directly affects human health, and few earth systems have a more controlling inuence on water quality than soil. Most water available to humans, namely groundwater accessed by wells or surface water in streams or lakes, passes through soil. Soil is capable of removing pathogens and toxic compounds from water. Soil stores water, which reduces ooding frequency and serves as a water resource reservoir. These processes are not unlimited, however. Society must understand the benets and limitations of soil to protect water resources for the benet of human health. Creative and strategic utilization of soil will continue to play a key role in sustainable maintenance of global water quality.