Abnormal rainfall this year has eased our concerns over drought, but climate change is increasing the likelihood of prolonged dry spells in our region. Around the globe, an increasing number of water-stressed cities are seeking ways to conserve and find new sources of water. One possibility is the capture and reuse of stormwater.

Growing demands for water, bigger populations, and longer dry spells are leading to more depleted aquifers. Researchers are exploring ways to replenish these underground reservoirs with urban runoff. Aquifer recharge is not new: Injection wells and infiltration ponds have long been used to direct water underground. For example, there are large basins around Los Angeles that direct hillside runoff into aquifers. Urban runoff from roads, parks, and rooftops is different, however, in that it is dirty, containing harmful contaminants from pesticides, blacktop, vehicle exhaust, grease, and oil, plus human and animal waste. The challenge is how to scrub out these contaminants before directing runoff water into underground reservoirs. 

Three promising approaches are being investigated. One technology is using a sand filter where the grains of sand are coated with a thin layer of manganese, one of the most common elements. The coating allows the grains to bind to and break down the chemicals found in herbicides and many consumer products as well as the endocrine-disrupting chemical bisphenol A. Over time, the sand loses its scrubbing effectiveness, but researchers have found a way to renew the potency of the sand filter by adding a tiny amount of chlorine — an amount similar to that used in treating most drinking water. 

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