By Dave Room and Ingrid Severson, Bay Localize

Rumsey EngineersRainwater catchment is an ancient practice used widely around the globe to harvest and store rainwater for human consumption and irrigation. Dating as far back as 4,000 B.C., it is now commonly used in Australia, New Zealand, parts of Europe, Japan, India, Sri Lanka and Thailand as well as the Caribbean, Central and South America.

With more than 250,000 practitioners in the U.S. alone, rainwater catchment is experiencing a revival in parts of North America including Alaska, Washington, Oregon, and Canada. Hawaii, North Carolina and the more dry regions of New Mexico, Arizona and Texas already boast government incentive programs. Although maintaining water supplies for increasing population demands is one of the California’s biggest challenges, the Golden state does not have government-backed, financial incentives for rainwater catchment.

photo credit: Rumsey Engineers

To get a perspective on California’s water challenges, it is instructive to take a look at the system upon which over 1.3 Million Bay Area residents rely for fresh water – the East Bay Municipal Utility District. EBMUD delivers water to Contra Costa and Alameda County from the Mokelumne River watershed in the Sierra Nevada foothills. The gravity-fed water travels about 90 miles from the Pardee Reservoir via the Mokelumne aqueduct system until it reaches the East Bay treatment plants and terminal reservoirs. The terminal reservoirs minimize flooding in local areas and regulate the river supply in Winter and Spring. They also augment EBMUD’s river supply by gathering watershed runoff and providing emergency supplies during extended drought and facility outages.

The Mukelumne River has been EBMUD’s primary source of water since the 1920s. But officials warn that the reserves and overall water system have many vulnerabilities and insufficiencies will eventually render them unable to meet the region’s growing water needs.

Many conditions affect the viability and reliability of this water system:

  • Evaporation and transpiration (i.e., the process by which water vapor escapes from the living plant, principally the leaves, and enters the atmosphere). In dry years, the volume of water they consume can exceed runoff into the reservoirs
  • Climate change studies generally conclude that average temperatures will increase in California, exacerbating drought conditions and thereby lowering runoff supplies to the reservoirs
  • Terrorism attacks to the levees
  • Levee vulnerability due to earthquakes and flood pressure
  • Limited reservoir capacity

Currently, EBMUD’s water rights allow for delivery of up to a maximum of 325 million gallons of water per day from the Mokelumne River. EBMUD’s water rights are relatively low in priority compared to prior right holders upstream. As reported by EBMUD, the existing Mokelumne River supply will continue to decrease in the future as diversions by water right holders in upsteam counties increase. Also, EBMUD is required to increase downstream releases for habitat protection as regulated by settlement agreements.

Water rights and these types of challenges facing EBMUD are endemic across California and the United States. Rainwater catchment offers one solution to these conditions by diversifying water supplies while also protecting watershed health. If every building in the Bay Area were equipped with a catchment system of a 1,000 gallon tank, stormwater flooding and (irrigation) water demand for utilities would be substantially lessened. Given the high upfront installation costs of this technology, financial incentives are a vital key for initiating water catchment to mainstream development.

The recent passage of Proposition 84 allows California to sell $5.4 billion in general obligation bonds, the proceeds of which go towards:

  • 28% – water quality
  • 27% – the protection of rivers, lakes, streams, beaches, and coastal waters
  • 19% – sustainable communities, climate change reduction, and forest and wildlife conservation
  • 17% – flood control and statewide water planning
  • 9% – parks and natural education facilities.

Rumsey EngineersA social benefit organization located in Oakland, Bay Localize, is advocating for a portion of Prop 84 funds to be used to create incentive programs for rainwater catchment on the basis of mitigating stormwater runoff, watershed protection, and increasing localized reserves of water for landscape irrigation, graywater, and emergency drinking supplies.

As a rule of thumb, each 1,000 square feet of roof area can produce up to 623 gallons of water per inch of precipitation. A newly designed home in San Francisco led by Lorax Development, features the city’s first approved rooftop rain catchment system that collects an average of 18,000 to 20,000 gallons of annual rainwater for residential and landscaping use. With this potential volume of water harvesting, large-scale cisterns could provide a sustainable resource for water supplies in our region.

photo credit: Rumsey Engineers

Sarah Sutton

Bay Localize’s Rooftop Resources Project explores the feasibility and promotes appropriate designs for mainstream use of rainwater catchment. The project is investigating the development of rain harvesting systems such as collective cistern use for multiple buildings in urban areas.

For more information or to volunteer, contact Internships are also available.

photo credit: Sarah Sutton

On a related note, the annual water conservation showcase is coming to San Francisco on March 25th

Attend the 5th Annual Water Conservation Showcase! March 25, SF
5th Annual Water Conservation Showcase
Tuesday, March 25, 2008, 10:00 am to 6:30 pm
Keynote presentation at 6:00 pm
at the Pacific Energy Center, 851 Howard Street, San Francisco, CA

Register here:

Join us for our 5th Annual Water Conservation Showcase. Many experts believe that water will surpass energy as the most notorious and coveted resource in California. Unpredictable levels of precipitation and other source issues, climate change, population growth, and risks to the infrastructure are some of the water-related concerns facing the state today. This year’s showcase will address many of these issues through presentations and table-top displays. Information on water-conserving strategies, the energy and water relationship, policy updates, technological developments, and case studies will also be included.