Rainwater Harvesting – Roofing, Gutters & Downspouts

The different components that make up a rainwater collection and harvesting system are:

  • Roof
  • Gutters & Downspouts
  • Screens, Filters
  • Storage Containers
  • Parts specific to the application
  • Water Disperal

Roofs and collection surfaces have the following characteristics:

  • Metal
  • Composition
  • Wood shingles – absorb water and stay moist longer
  • Tile roofs – absorb more water
  • Solar Panels – best surface
  • Acrylic coating over old tin
  • Older roofs – lead

You should ensure your roofing material is slick in order to reduce debris, avoid pooling and you should consult the NSF protocol P151 to find approved coating for your roof.

The slope of your roof plays an important part in determining your rain collection approach –

Steep roofs:

  • Water drains off faster
  • Cleans contaminants off  quicker
  • Gutter has to have the ability to stop and transport the water faster

Flat Roofs:

  • Water moves more slowly
  • Contaminants are very slow  to run off

Gutters & Downspouts

  • Smooth
  • Durable
  • Attractive
  • Well suited to the building
  • Correct Size and meets Uniform Plumbing Code (UPC)


  • Materials – vinyl, seamless aluminum gutters, galvanized steel, stainless steel, copper
  • Slope towards the downspout of 1/16″/1′ to 1/16″ per 10′
  • Titled out – 1/2″ to prevent water seeping into walls
  • Expansions joins for runs over 40′
  • Hangers every 3′
  • Valleys-splash guards
  • Number of downspouts – varies with size and surface area – 1 per 1,000 square feet surface
  • 1 square inch of outlet per 100 square foot of roof surface


  • Schedule 40 ABS
  • Schedule 40 PVC
  • Copper
  • Cast Iron
  • Aluminum
  • Galvanized Steel

Downspouts should be spaced 20 to 50 feet apart and 45 degree bends should be used as oppose to 90 degree bends whenever possible. The requirements are 1 in squared of downspout of every 100 feet squared of roof.

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