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How Much of Today's Precious, Precious Rainwater Do We Actually Get to Keep?

Not enough.


San Francisco might be great at conserving water, but we're hopelessly terrible at catching it out of the sky. According to the city, today’s rainshowers are quite literally trickling through our drought-parched fingers. Being an urban environment with a whopping 1,260 miles of streets, San Francisco in large part lacks the ability to absorb rainfall. Which means that most of that precious, precious water that fell on the city this morning (approximately one-third of an inch, for those counting at home) is sliding right down the storm drain.

Rainwater catchment, though popular with a handful of schools and homeowners, is “not a system-wide approach” in the city’s sewer system, says Jean Walsh, spokesperson for the San Francisco Public Utilities Commission. The commission’s Civic Center building is one bright exception, though: It sports rooftop cisterns that can capture 25,000 gallons at a time, which then goes toward irrigation. 

“Schools have also been early adopters,” says Walsh. “And people are installing systems in their backyards,” forming an ad-hoc network that catches a very small percentage of San Francsico’s rain, she adds. The commission is currently loaning out 50-gallon rain barrels free of charge to residents of single-family and two-unit homes. 

Trapping rainwater is much bigger endeavor farther south, where irrigation districts are slicing up the earth in anticipation of El Niño rains, according to the LA Times. Groundwater banking, as it’s called, is a strategy for capturing floodwater that’s cheaper, albeit much less predictable, than building reservoirs (gravity doesn't exactly take orders from bureaucrats, it turns out). 

Strategies for capturing rain and floodwaters will become more important as climate change deepens, the LAT points out, because of how much more of our precipitation will fall as rain, not snow. Snow melts in the spring and releases its moisture slowly in the drier season, but converting that snow into rain—if we’re lucky to get it at all—often means losing water as runoff.

At the very least, though, we’re cleaning the rainwater before sending it back into the ocean. San Francisco has a combined sewer system, which means that runoff from the streets gets treated right alongside the rest of the city’s waste in the sanitary system. So we can pat ourselves on the back for not sending a bunch of heavy metals and other contaminants to Ocean Beach as we let all that water slip away. Hooray?


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