Whether you are designing your own rainwater catchment system or having one designed by a professional, success of your rainwater catchment system design is dependent on some key factors.

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What do I want to accomplish with my design of a rainwater catchment system?

Irrigation, toilet and or laundry facility, supplementary to well water or city water, whole house usage, and sole source are the main purpose of designs.

How much rainwater can I collect from my roof? Will it be enough to supply my needs?

One inch of rainfall per 1,000 square feet of roof will yield approximately 623 gallons of water. Evaporation, wind, and spillage account for 15 – 20 % of loss. A 2,000 square foot roof with 36″ of annual rainfall may yield 44,856 gallons. With an efficiency of 85%, that equals 38,128 gallons.

One inch of rain is needed for the healthy growth of plants. This equates to .623 gallons per week for 1 square foot of planting, which can add up rather fast, so keeping your irrigation needs small and giving consideration to drought tolerant plants is recommended.

Toilet and laundry facilities account for 49% of household usage. Designing and building a system for this purpose alone can cut your water and sewer bill in half. New construction is the best time to implement this type of system however, retrofitting plumbing in an existing home can be accomplished.

If the collection area is small or available space for storage is restricted, a supplementary system can be achieved with “slim line” style of cisterns or buried tanks. A small roof can still be effective in collection if used for a supplementary source to well water or city water.

Whole house usage, or potable water, can eliminate dependency on city water or well water, where you can still have city or well water as a back up during dry times. With the advanced filtration and UV disinfection offered today, safe, reliable drinking water for whole house usage will exceed the quality of most well and city water.

Now that you are considering what usage of collected rainfall would best suit your needs, we will discuss sizing, configuration, implementation, and maintenance of a designed rainwater catchment system in upcoming posts.

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Ken Blair

President at RainBank Rainwater Systems

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.