City of Bellingham, Washington's water harvesting guide, which focuses on active water harvesting: http://wrrc.arizona.edu/sites/wrrc.arizona.edu/files/Bellingham_Rainwater%20harvesting%20manual.pdf
National Resources Defense Council report that discusses the potential of active and passive water harvesting: http://wrrc.arizona.edu/sites/wrrc.arizona.edu/files/NRDC_Capturing%20Rainwater%20from%20Rooftops.pdf