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When designing or implementing your system be sure to follow the principles for cistern systems described in Rainwater Harvesting for Drylands, Volume 1.

Click here to read an article about a Cockrell School of Engineering study comparing different roof types to see which are best for harvested-rainwater quality. Click here for the study itself.

Energy Star-Compliant Roofing & Cool-Roof Savings & Tax Credits

The EPA estimates Americans spend about $40 billion annually to air-condition buildings, while expending one sixth of all electricity generated in the U.S. to do so.

  • ENERGY STAR-qualified/cool-roof products reflect more of the sun’s rays. This can lower roof surface temperature by up to 100F, decreasing the amount of heat transferred into a building.
  • ENERGY STAR-qualified/cool-roof products can help reduce the amount of air conditioning needed in buildings, and can reduce peak cooling demand by 10-15 percent.
  • During building design and when your existing roof needs replacement are both excellent times to consider reflective roofing.

Follow these links for information on Energy Star-Compliant Roofing and Cool-Roof Savings, and Tax Credits.

For more info see the Florida Solar Energy Center study and report, “Comparative Evaluation of the Impact of Roofing Systems on Residential Cooling Energy Demand in Florida.”

And for more info on how you can integrate the orientation of your building and its landscape with on-site water-harvesting and food-production strategies, as well as ideal roof-overhang design to further maximize the efficiency and production potential of your roof, read Rainwater Harvesting for Drylands and Beyond, Volume 1, 3rd Edition.

Metal Roofing

Be sure roofing is at least 26 gauge (26 or lower), since lighter gauges (higher numbers indicate thinner materials) can dent. Baked-on enamel, galvanized, and galvalume steel roofs all work with water harvesting systems.
List of contractors, distributors, and manufacturers across the country.

Mueller, Inc.
Lap-style corrugated, U Panel, R Panel, and AP panel metal roofing.

ASC Building Products

MasterCraft Metals, Inc.

Standing Seam Roofing
(800) 607-7468
(520) 792-2418

Roof Ops Roof Options
Corrugated, Galvanized, Rusted, R Panel, Metal Tile, Metal Shingle
(520) 318-4364

Allied Building Products
(520) 795-7663

Elastomeric Paint Approved for Potable Rainwater Catchment Systems

The following have been tested and certified by the National Sanitation Foundation International (NSF) as approved potable-water-catchment coatings that comply with the requirements of NSF Protocol 151 “Health Effects from Rainwater Catchment System Components” (

Weather Barrier Rain Coat 2000
An acrylic roof coating for pitched roofs that can be applied over an existing roof of less-desirable materials such as asphalt shingles. Due to its light color it is also effective in passively cooling buildings. Manufactured by Finnaren & Haley Inc., Conshohocken, PA.

Topcoat W. O. B. White (without biocide)
A water-based liquid that can be applied with a brush, roll or spray mechanism. It cures to form a seamless rubber membrane that covers the entire roof. Topcoat W. O. B. White (without biocide) is manufactured by Topcoat, Inc. a subsidiary of GAF Materials, Inc., Walpole, MA. Note: Topcoat W.O.B. is produced in the Caribbean, and while readily available there, it can be difficult to obtain in the Continental United States. Per site user EF Doyle, Cerrillos NM: The working numbers here are 877 423 7663 and 800 766 3411 there is a representative in New Mexico, Chris Dimas, that can also help 505 417 4355. He might need to call local suppliers as the products are not well known. Internet searches for TopCoat and GAF Materials will lead to many disconnected numbers. This product cannot be used on any asphalt or shingle roof applications — it is good for metal and concrete applications.
(800) 669-4128

Vulkem 450/451 PWC and Vulkem 450/451 PWC Red
Elastomeric paints rolled or brushed onto a roof surface. According to a representative of the manufacturer the products are currently used in Bermuda and the Virgin Islands, but may be difficult to acquire within the continental United States. Manufactured by Tremco Incorporated, Mameco Manufacturing Division, Cleveland, OH. Per site user EF Doyle, Cerrillos NM: This product has been replaced with 350 SL primer and 351 cover coat. It is not good on TPO or shingle roof systems.
(216) 752-4400

2001 Super-Flex 100% Acrylic Elastomer Roof Coating, 3000 Acrylic Barrier Coating, and TK2001 Elastomeric Finish
All 3 products are manufactured by the Scott Paint Company, Sarasota, FL. Per site user EF Doyle, Cerrillos NM: The product here is the 2001 Super-Flex, the other names do not seem to be known to the folks at corporate or their main distribution point. The 2001 is good on asphalt, metal, TPO roof applications. They do not have distribution so people will need to arrange their own shipping. We found three online freight brokers that cost us less than $300 to ship to Santa Fe, New Mexico from Sarasota (Freight Quote — Ms. Kim Richenback; Discount Freight — John; and Priority1 — David). UPS would have been $1100. For technical assistance and to order, call Larry at (941) 379-6428.

Elastomeric Paint Not Yet Certified by Neutral Third Party for Potable Rainwater Catchment Systems

The manufacturers of the following products claim they are fine or are likely fine as a roof surface with potable rainwater catchment systems. However, the following products have not yet been certified by a neutral third party, such as NFS, as approved for potable rainwater catchment systems.

AMES Blue Max

We NO LONGER recommend this product for use within water tanks.
It is a blend of adhesive elastomeric liquid rubber. The manufacturer claims it is a new impenetrable rubber technology for waterproofing in extreme wet situations such as flat roofs, below-grade foundations, basement walls, cisterns, water troughs, catch basins, ponds and fountains. However Watershed Management Group in Tucson, Arizona, has found BlueMax does not maintain a seal in tanks. WMG’s Catlow Shipek reports, “When submersed in water it is common for blisters to form as layers separate either from each other or the surface it is applied to. It also seems to re-emulsify slightly.”

Additional notes: Water coming in contact with Blue Max can be expected to have a slight chemical flavor. Also, this product is NOT certified for potable water systems by neutral third-party institutions such as NSF, though the manufacturers claim it is safe for use in potable rainwater catchment systems.

A continuous-filament, single-ply, fluid-applied roofing system. It is a non-petroleum-based polymer. Due to its white color it is energy efficient in hot climates.  It has been tested and certified by the FDA 175-300 as approved for Direct Food Contact.

Safecoat Dynoflex RoofGuard Elastomeric Roof Coating
A water based, low odor roof coating suitable for properly primed roofs. The manufacturer has verified that this product is:
– Lead-free
– Mercury-free
– Cadmium-free
– Copper-free
– Antimony-free
This likely makes it a Living Building Challenge-compliant product. The Living Building Challenge is a Green Building Certification that goes well beyond LEED. The product is currently manufactured in Los Angeles, California, by American Formulating & Manufacturing.

Reinforcing Fabric Often Used Beneath Elastomeric Roof Coatings Is Often Toxic

You can read about Brad’s unfortunate discovery here.

Rainwater Harvesting