Diagram of a water tank filtration and flow system with ball valve.
How-to, Rainwater Harvesting Education

What is a First-Flush Diverter?

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This post is part of the series How to Build a Simple Rainwater Collection System.

A rain barrel system attached to a house downspout for water collection.A first-flush diverter helps keep your rainwater harvesting system clean byenabling the removal of dust, other debris, and any fecal matterthat collects on your roof and in your guttersbetween rainfalls, so it is flushed out at the verybeginning of the water collection process.

Diagram of a water tank filtration and flow system with ball valve.
Click to view larger version of First Flush Diverter Diagram

Thecleaner your water is as it goes into yoursystem, thecleaner your water will be when you use it. Studieshave shown a tremendous drop in fecal bacterialevels when the roof is flushed before water entersthe tank. Bacteria also like to live in decaying leavesand other organic matter that collects at the bottomof the tank. A first-flush diverter “washes” the roof,so there is less rubbish on the tank’s bottom.

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Ken Blair
A rainwater collection systems designer and consultant, Ken has designed and installed residential and commercial systems, primarily in the northwest United States for more than 10 years and, in 2014, began consulting and managing builds in other states. Ken is an accredited ARCSA Professional Designer / Installer and Life Member, the Northwest Regional ARCSA representative and advisor to its education committee and is available to speak about Rainwater Collection Systems design and builds.

Ken is a United States Navy veteran, having served on active duty during the Vietnam War era.

A career entrepreneur, Ken created a new business focus with a commercial dive company in Hawaii in the mid 1980′s to respond to and clean up oil spills, oil spill equipment training, service and maintenance for the oil co-op service industry. Ken is passionate about having a positive impact on the environment and is also a founding director of BANK-ON-RAIN (2011-2014), whose mission is to create grassroots solutions for rainwater collection for consumption and agriculture in developing areas of the planet.