Date: 07/27/2010

Category: · Writing  » News Coverage  » Streetsblog · Writing  » Topic  » science

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When most San Franciscans turn on a faucet, they'll see water that's traveled as far as two hundred miles from Hetch Hetchy Valley in Yosemite National Park. But that's not the case for some locally-minded gardeners, for whom careful water stewardship is as important as selecting their crops.

This past weekend, the San Francisco Bike Coalition organized a rec ride that visited several gardens around the Sunset, highlighting low-impact water sources. The ride was led by Sarah Roggero of TransitionSF, an organization that promotes a locally-sourced lifestyle as an alternative to dependence on fossil fuels.

Garden for the Environment

The tour began at Garden for the Environment, a pocket of green on 7th Avenue just a few blocks north of Laguna Honda Reservoir. Executive Director Blair Randall grabbed handfuls of earth, squeezing the soil into a ball to show the roughly three dozen attendees how healthy soil should clump.

In San Francisco, Blair explained, gardeners will need to provide their plants with supplemental water during the dry summers. Even native drought-tolerant plants will benefit from a little assistance, around half a gallon per plant per week. Vegetables and fruit trees will need more, he added -- theirs receive much as fifteen gallons per week, some of which comes from rainwater catchment barrels. A modest installation alongside a greenhouse collects water during storms, then parcels out the moisture during dryer months.

The San Francisco Public Utilities Commission recently completed a highly successful rebate program to encourage residents to install their own rainwater collection systems. Although the rebate has ended, the PUC continues to encourage the practice, offering instructions and a video tutorial for building your own. Organizations like Greywater Action offer further training and workshops.

Blair recommended that gardeners use drip-irrigation: a thin tube, perforated with small holes, slowly releases water close to the roots. In contrast, sprinklers lose much of their water to wind, evaporation, and weeds. Compost, manure, wood chips, and straw also help keep moisture close to the roots.

He also advised that gardeners observe and exploit San Francisco's natural advantages -- for example, planting in the fall to take advantage of the rain, and favoring Mediterranean plants like artichokes. It's important to keep an eye out techniques and species that prove successful, since every garden is unique.

"The key to success as a gardener," he said, "is your power of observation."

Blair describes water usage at Garden for the Environment. Photo: Matt Baume.

Reservoir History

From Garden for the Environment, the caravan of bikers travelled west to the Sunset Reservoir, a 270-acre, 88-million-gallon tank between 24th and 28th Avenues.

The reservoir, built in the 1960s, showcases some modern low-impact technology: newly-installed panels on the roof have tripled the city's solar power generation, and starting in 2013, the PUC plans to introduce locally-sourced groundwater. That local water could prove vital if an emergency cuts off the city's distant water sources.

Historian and explorer Joel Pomerantz stood in front of the massive slab of the reservoir, describing the city's many natural water sources. Mountain Lake, for example, was an early source of potable water for San Franciscans, with a flume reaching all the way around Fort Mason to what is now the Marina.

Today, our water is derived largely from Hetch Hetchy, as well as reservoirs on the Peninsula and in the Alameda watershed.

All of San Francisco's water sources are controlled by the Public Utilities Commission, said Pomerantz, which he sees as a potential problem. "The more water systems the PUC is in charge of, the more it's a centrally controlled system," he said, explaining that a more independent, neighborhood-based authority would guard against what he called "political control."

Our modern central authority is a far cry from San Francisco's early days, when dozens of wells dotted the city. "We don't allow people to just dig up their own wells," confirmed SFPUC spokesperson Tyrone Jue. "They would have to get a permit. ... We'd talk to them. It's all about public health at that point." A few local wells remain in use for irrigation purposes, such as at the San Francisco Zoo and in Golden Gate Park.

But drilling down to the aquifer -- about three hundred feet, out in the Sunset -- is expensive, as is testing the water to ensure health. "If you had a personal well, we'd have to make sure you were meeting the testing requirements," said Jue. "And it just becomes so onerous at that point ... why would you?"

Jue added that sources for fresh water in the city disappeared as the city grew increasingly paved. "Before the city was paved over, you'd have the natural creeks running down from Twin Peaks, and they'd go out into the bay. But since we've paved over the entire place, all the water is captured in the sewer system at the source. The stream never forms in the first place."

Residential Solutions

A garden featuring greywater and humanure. Photo: Matt Baume.

Next, the bicycle caravan headed to the ocean, stopping in at the beach-adjacent home of Christina and Tim, two hardcore backyard gardeners. They welcomed the group by recommending that the riders try out their composting toilet.

Although the garden featured several creative installations -- a sweat lodge, a passive-solar shower, reclaimed laundry water -- it was the composting toilet that drew the most questions. Though unfamiliar to most, "humanure" is nothing new: a big bucket, a little sawdust, some micro-organisms, and patience are the chief requirements for a system that doesn't smell, doesn't breed parasites, and doesn't contaminate surrounding areas.

It takes about a year before humanure is sufficiently broken down and rid of potential contaminants. Additional precautions are often necessary: in chilly environments like the outer Sunset, urine has to be diverted into a separate storage tank.

In addition to their composting toilet, Christina and Tim (along with their two housemates) also recycle their laundry water. The process begins with a biodegradable detergent like Ecos; from there, the water is channeled into a bathtub full of cattails. The wetlands plants filter out contaminants, just like the bioswales that are appearing around the city in ever-increasing numbers.

After some tinkering, the system has produced a slow trickle of naturally-scrubbed greywater, suitable for garden use, with laundry residue left behind in the plants. "You wouldn't want to eat those cattails," laughed Tim.

Most San Franciscans probably aren't ready to reconfigure their washing machine or forgo their flush-toilet. But rain barrels are inexpensive, relatively easy to operate, and a fun DIY project.

And as Christina pointed out, the act of just thinking about water usage can itself be productive. She recently conducted a study of household water usage, and found that when people pay attention to the volume of water that we flush, spray, and dump, wanting to cut back is a logical next step.

With water imported from far-flung artificial lakes and a sewer system with a habitual overflow problem, a little lateral thinking about water might be just what we need.