Precipitation fills our streams and lakes and soaks into the ground to replenish our aquifers. Most moderate rainfall is readily absorbed by soil, which acts as a natural filter as water moves through the cycle. But, in heavy storms, excess moisture can run off oversaturated ground. Because we’ve engineered so much of our land with impervious surfaces, that runoff can be excessive. Without the benefit of natural filtration, stormwater flows directly to waterbodies, storm drains, and sewer systems, taking with it any debris, chemicals, bacteria, eroded soil, and other pollutants it picks up along the way.
While new technologies and green infrastructure help reduce pollutant levels, many solutions are best equipped to handle frequent, low-intensity storms, rather than the sporadic, powerful storms experienced more recently. To compound the problem, population growth and rising water demand have increased dependence on local water sources, including groundwater recharge—raising more concern over potential contaminants.