HarvestH2o Online Community

Rainwater Harvesting & Plumbing Codes

by Susan R. Ecker, Senior Plumbing Engineer, Rumsey Engineers

United Nations projects that by 2025 waterstressed regions will encompass two-thirds of the countries in the world. The U.S. has already joined China, India, northern Africa and the Middle East as a country that now faces severe imminent water shortages.

In the U.S., we routinely design buildings that use clean drinking water for flushing toilets and for landscape irrigation. With the evolution of green building practices, more emphasis is being placed on water conservation in building design. Widely practiced measures include specifying low- flow toilet fixtures such as dual-flush toilets, sensor-operated lavatories and zero-water consumption urinals. Other measures include the use of gray water, reclaimed water and rainwater harvesting (rainwater catchment). Stored rainwater collected from a large catchment surface (such as that provided by the roof of a typical commercial building) is a cost-effective source of water for landscape irrigation and toilet flushing. The use of rainwater as a domestic-water source not only decreases the amount of clean drinking water used by a building, but it also decreases the amount of storm water runoff from the site, which in turn, lessens its affect on erosion and decreases the load on storm sewers.

The Uniform Plumbing Code (UPC) and the International Plumbing Code (IPC) do not directly address rainwater harvesting systems in either the potable water or storm water section of the code. Appendix J of the UPC reclaimed water—some jurisdictions enforce this portion of the code for rainwater harvesting systems. It is important to note that rainwater harvesting systems are not reclaimed water systems. The difference will be explored in greater depth later in this article. Many local jurisdictions provide guidance in the design of rainwater-harvesting systems. This is an area where the code writing bodies must quickly adapt to the realities of the building industry and the water shortage crisis throughout the world.

The U.S. may not be at a critical stage now, but global climate change has the potential to significantly decrease snow pack as well as the seasonal snowmelt, which fills our reservoirs, keeps our tap water flowing and our farmlands irrigated. The U.S. was built on the assumption that unlimited water resources were available—an assumption that was clearly flawed. The need to conserve and reuse water will only continue to intensify.


Cisterns are an ancient technology. In the Middle East in 2000 B.C., typical middle-class dwellings stored rainwater in cisterns for use as a domestic supply as well as private- bathing facilities for the wealthy.

The world’s largest cistern may be the Yerebatan Sarayi. On the European side of Istanbul in Turkey, it was constructed under Caesar Justinian (A.D. 527-565) and measures 140 by 70 meters. It can store 80,000 m³ water. The underground structure is based on intersecting vaults. Today, it is a tourist attraction which is visited by boat, drifting through a forest of columns. Another cistern in Istanbul is called Binbirdik, believed by some sources to have been constructed under Caesar Constantine (A.D. 329-337), with a capacity of 50,000 m³. Each cistern served as centralized storage for water collected from roofs and paved streets and featured a sophisticated system of filters that assured clean water.

These municipal underground cisterns may be the only examples of urban centralized rainwater harvesting of their kind. This technique was likely abandoned for two primary reasons: 1) the construction of underground cisterns is considerably more expensive than the construction of dams; 2) there is a danger of accidental pollution through human excrement in dense urban areas and a corresponding risk of epidemics.

Water Classifications

Harvested rainwater is shrouded in confusion. Some jurisdictions consider it reclaimed water and others refer to it as gray water. Actually, it is neither. To clarify, UPC offers the following definitions.

• Black water is toilet waste.

• Gray water is untreated wastewater that has had no contact with toilet waste such as used water from bathtubs, showers, lavatories and water from washing machines. It does not include wastewater from kitchen sinks or dishwashers.

• Reclaimed water is water which, as a result of tertiary treatment of domestic wastewater by a public agency, is suitable for controlled use. The controlled use can be the supply of reclaimed water-to-water closets, urinals and trap seal primers for floor drains and floor sinks. In areas under the jurisdiction of the UPC this system is usually called a “purple pipe” system because the reclaimed water is conveyed in pipe that is purple.

• Harvested rainwater is storm water that is conveyed from a building roof, stored in a cistern and disinfected and filtered before being used for toilet flushing. It can also be used for landscape irrigation.

As noted, Appendix J of the UPC describes reclaimed water, but according to the above definition, rainwater harvesting is not reclaimed water. Plumbing officials who do not know how to classify rainwater-harvesting systems consider them reclaimed water systems and therefore require plumbing engineers to design systems that conform to Appendix J of the UPC. This is because of the lack of guidance in the code. Since these systems are becoming more prevalent in the U.S., both the UPC and the IPC must include a section dedicated to rainwater harvesting.

Rainwater Harvesting Basics

The components of the rainwater-harvesting system include:

Roof. Rainwater should only be collected from a roof and stored in a cistern. Rainwater runoff from parking areas and other outdoor surfaces typically contain harsh chemicals and other contaminants that are undesirable in a rainwater catchment system.

Rainwater conductors. Leaders and gutters or an internally piped roof drainage system that conveys the storm water from the roof to the cistern.

Cistern. A storage tank that allows large particulate matter to settle out of the water.

Overflow from cistern. A pipe that takes overflow from the cistern to the storm drainage system.

Pumping system. Provides the pressure required at the fixture most distant from the tank.

Disinfection system. Various filtration and disinfection systems can be used.

Potable water makeup. Makeup water provided to the tank during dry seasons. Appropriate backflow prevention is required.

Rainwater from the roof is directed to either an internally piped roof drainage system or to gutters and downspouts, and conveyed to a cistern. Before reaching the cistern, the water should be filtered to remove large contaminants such as leaves, twigs and other organic matter. The cistern or storage tank should be capable of being filled from both the rainwater-harvesting system and the domestic-water system. The cistern can be located above or below grade, and should feature a manhole for maintenance purposes. Cisterns should be protected from direct sunlight to prevent the growth of algae and other microorganisms. Cisterns should be equipped with overflow pipes, and rainwater overflow should be piped to the storm system. During the dry months it may be necessary to use domestic water as a backup to rainwater usage. Depending on the requirements of the Authority Having Jurisdiction (AHJ), an air gap and/or a reduced-pressure backflow preventer will be required to prevent cross-contamination between the rainwater and the domestic water. Consult with the local plumbing inspector during the design phase of the project to define the requirements for the project.

Health Issues

Although bacterial contamination of water for indoor nonpotable use is not as critical as that of potable purposes, total coliform and focal coli form sampling can be performed to evaluate a general level of acceptable microbial contamination for nonpotable water. The acceptable level of total coliform for nonpotable water should be less than 500 colony forming units (cfu) per 100 mL, and fecal coliform levels should be less than 100 cfu per 100 mL. Testing is recommended on an annual basis.

A potential health issue can arise if a cross connection is created between domestic water and rainwater. Health issues can be avoided by installing the makeup water to the cistern with an air gap of at least 2 in., and/or providing a reduced pressure backflow preventer as per the AHJ. Some plumbing inspectors are so concerned about the contamination of the potable water that they request both an air gap and a reduced-pressure backflow preventer—which can be likened to wearing both a belt and suspenders—your pants will definitely stay up. That said, if it is an AHJ mandate, it must be provided.

Proper labeling of the system piping will help to prevent cross connections during future building renovations. Piping should be labeled to show that the liquid is rainwater and not for drinking. The labels should be located on piping in walls, within ceiling spaces and on exposed piping.

Recent studies conducted in Germany have shown that although the quality of rainwater in reservoirs generally does not meet the quality of potable water, it is extremely well suited for domestic uses such as flushing toilets. One study took several billion fecal bacteria and mixed them in a toilet bowl with the water from of rainwater reservoir, which has a maximum concentration of 10,000 E. coli per liter. According to the literature, the probability of a single bäcterium reaching the vicinity of the human mouth during the flushing action is in the order of approximately 1:1,000,000. From this the study concludes that the possibility of any E. coli reaching the vicinity of the human mouth when toilets are flushed can be virtually excluded. These studies were performed to demonstrate that no special disinfection measures were necessary for rainwater to be used for non-potable water functions.

In the U.S., filtration and disinfection of rainwater for potable water use is commonplace. Several different disinfection processes are used such as:

Particulate filter(s) with an ultraviolet disinfection unit. Filters must be changed and the unit must be cleaned periodically.

Ozone. The ozone acts as a powerful oxidizing agent that reduces color, eliminates foul odors, and reduces total organic carbon in water.

Chlorine. Automatic self-dosing systems are available. A chlorine pump injects chlorine into the water as it enters the building. Appropriate contact time is critical to kill bacteria.


While no national standards currently exist for the design and installation of rainwater-harvesting systems, some state and local ordinances have been written to address them. Ohio, Kentucky, Hawaii, Arizona, New Mexico, Washington, West Virginia, Texas and the U.S. Virgin Islands are a few of the jurisdictions that have developed or are considering developing codes and standards for harvesting systems. The UPC and IPC should address the issue of rainwater harvesting and provide guidance to the design community on a national level.

Uniform Plumbing Code (UPC) and International Plumbing Code (IPC)

Neither the UPC nor the IPC address rainwater-harvesting systems. Some code officials have requested that purple pipes be installed inside the building when a rainwater-harvesting system is installed. This would certainly prevent the future connection of a domestic water fixture to this piping. but as evidenced by the definitions provided above, a rainwater system is not a reclaimed water system.

Both the UPC and IPC have a section that deals with alternate materials, methods and equipment. Section 301.2 of the UPC (similar to Section 105.2 of the IPC) slates, “The provisions of this code are not intended to prevent the installation of any material or to prohibit any method of construction not specifically prescribed by this code, provided that any such alternative has been approved. An alternative material or method of construction shall be approved where the code official finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, and least the equivalent of that prescribed in this code in quality, strength, effectiveness, fire resistance, durability and safety.”

This section provides the code official the flexibility to approve the installation of a rainwater-harvesting system. The design engineer must submit an application, available through the building department, known as an alternate materials and methods request (AMMR). Approval is granted on a case-by-case basis.

Alternate Materials & Methods Request

A checklist may be helpful when planning and preparing for the approval process of AMMR.

  • Start early. Identify as many of the nonstandard aspects of the project as early as possible.
  • Gather Information. Become familar with local permit process requirements and the current codes and standards that will apply to your project.
  • Gather information about the specific alternatives. Try to collect technical reports, test results, books, authoritative publications, videos and documentation of the successful use (and approval) of the alternative in other places.
  • Enlist help. Seek out and, when necessary, engage knowledgeable experts and resource people, including sympathetic code officials, to support your position.
  • Take the high road. Consider the building department to be a resource, rather than an adversary. Maintain a cooperative, open-minded and positive attitude, acknowledging also that the building officials have the authority to approve alternatives that meet the intent of the code.
  • Pay attention to the relationships. This is partly a process of creating trust, both in your design approach and in your willingness to meet the intent of the code, having a good relationship with the building department can be a big help.
  • Meet and share information with building officials. Arrange an initial meeting to formally discuss the project and proposed alternatives. Try to include the decision-makers and any sympathetic officials or inspectors you may have identified.
  • Get specific feedback from a building official. Expect questions, objections, and issues to be raised about the proposed alternatives, both during (or following) the initial meeting and again when the plans are submitted for approval.
  • Address concerns and objections with reasonable and factual responses. This is an area where the influence of another code official familiar with the proposed alternative -- and supportive of it -- can be of enormous benefit.
  • Network. The most valuable of these are often the experienced building officials who have approved and worked with the materials or methods in question, or who are open-minded and receptive to alternatives.
  • Show perseverance and patience. It is important for the building department to understand that you will not be easily discouraged.

If you don't get the approvals you seek, there are several options to choose from. Here are a few:

  • Hold harmless legal documents. Offer the jurisdiction a letter or legal document, which holds them harmless and absolves them from all responsibility for the alternative materials and methods used.
  • Reminder of licensed engineer’s assumed responsibility. The argument can be raised that the engineer has stamped the plans and has already taken legal responsibility for the design when they placed their professional seal on the plans. This is a fact that is often ignored by building departments.
  • Local appeals process. At the request of any denied applicant, the codes provide for an appeal process oin which the building department must convene an appeals board meeting
  • Political pressure. As a last resort, political pressure can be applied either through the jurisdiction’s elected officials or through media attention with a story in the paper on television or radio. Publicity and political pressure can be effective tools to gain your immediate goals, sometimes even long-term change, but they should be pursued very carefully, because they can also result in lingering resentment and long-term resistance.

Celebrate, offer thanks, and share what you've learned.


As water shortages become more prevalent in the U.S., rainwater-harvesting systems will become more essential. The UPC and IPC must be updated to include these important water-conserving systems. If water-efficient technologies are incorporated at the code level, the resulting cumulative effects on water conservation across the country will be significant, as market opportunities open up for new products, customers demand more water-efficient designs, and designers face less resistance to incorporating efficient systems in buildings. Until they are included in the plumbing codes, it is up to the plumbing engineer to specify them and work with building officials in order to help conserve our increasingly scarce water resources. We can live without oil but we cannot live without clean drinking water.

Copyright © 2007 TMB Publishing
Reprinted with permission from Plumbing Engineer and Susan R. Ecker
Vol. 35, No. 3. Visit www.plumbingengineer.com

Update: Since the writing of this article in 2007 the codes have moved forward. UPC and IPC have both worked on inclusion of green building technologies; including rainwater harvesting.

More Info and Links






Rain Harvesting

Xerxes Tanks

Fun Facts


Taking on Water

A Great Aridness

Drinking Water

Tapped Out


ABOUT US -|--FAQS -| -MORE ARTICLES -| -RESOURCES -| - VENDORS |- NEWS-|- NEW PRODUCTS -| SERVICES Copyright © 1990-2022 HarvestH2o, All Rights Reserved 505-603-5498