Rainwater Harvesting and the Plumbing Codes

By Susan R. Ecker, Senior Plumbing Engineer

Rumsey Engineers

By 2025, the United Nations projects that water stressed regions will encompass two thirds of the countries in the world. The United States has already joined China, India, northern Africa, and the Middle East as a country that now faces severe imminent water shortages. (1)   

In the United States we routinely design buildings that use of clean drinking water to flush 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 decreases the amount of storm water runoff from the site, which consequently lessens its effect 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. The UPC has Appendix J which deals with reclaimed water  - some jurisdictions enforce this portion of the code for rainwater harvesting systems. It’s important to note that rainwater harvesting systems are not reclaimed water systems: this 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 need to quickly adapt to the realities of the building industry and the water shortages faced all over the world today.

We may not be at a critical stage in the United States now, but global climate change  has the potential to significantly decrease snow pack and the seasonal snowmelt which fills our reservoirs and keeps our tap water flowing and  farmlands irrigated. Our country was built on an assumption of unlimited water resources - we now know that this assumption was flawed. The need to conserve and reuse water will only continue to increase.

History

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

Probably the world's largest cistern is 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 metres. It can store 80,000 m³ water. The underground structure is based on intersecting vaults. Today it’s a tourist attraction which is visited by boat, drifting through a forest of columns. Another cistern in Istanbul is called Binbirdik , thought 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.

But these municipal underground cisterns are probably the only examples of urban centralized rainwater harvesting of their kind. There are probably two major reasons why this technique was no longer used. First, the construction of underground cisterns is considerably more expensive than the construction of dams. Second, there is a danger of accidental pollution through human excrement in dense urban areas and a corresponding risk of epidemics. (2)

Water Classifications

There is considerable confusion about what harvested rainwater is. Some jurisdictions consider it reclaimed water and others refer to it as “graywater.” Actually it is neither. In order to clear up the confusion, I provide some definitions from the UPC:

• Black Water is toilet waste.
• Graywater is untreated waste water that has not come in contact with toilet waste. Graywater includes used water from bathtubs, showers, lavatories and water from clothes washing machines. It does not include waste water from kitchen sinks or dishwashers.
• Reclaimed Water is water which, as a result of tertiary treatment of domestic waste water by a public agency, is suitable for a 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 in color.
• 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.

Appendix J of the UPC deals with reclaimed water, but according to the above definition, rainwater harvesting is not reclaimed water. Plumbing officials that 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 due to the lack of guidance in the code. Because as these systems are becoming more prevalent in the United States, both the UPC and the IPC need a section dedicated to rainwater harvesting.

Rainwater Harvesting Basics             

The components of the rainwater harvesting system are:

• Roof - Rainwater should only be collected from a roof and stored in a cistern. Rainwater runoff from parking areas and other outdoor surfaces typically contains harsh chemicals and other contaminants which 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 either to 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 so that large contaminants such as leaves, twigs, and other organic matter are removed. 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 either above or below grade, and a manhole should be provided for maintenance purposes. Cisterns should be protected from direct sunlight, in order 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 utilize 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 in order to prevent cross-contamination between the rainwater and the domestic water. Consult with the local plumbing inspector during the design phase of the project in order to define the requirements for the project.

Health Issues

Even though bacterial contamination of water for indoor non-potable use is not as critical as that used for potable purposes, total coliform and fecal coliform sampling can be used to evaluate a general level of acceptable microbial contamination for non-potable water. The acceptable level of total coliform for non-potable water should be less than 500 Colony Forming Units (CFU) per 100 milliliters, and fecal coliform levels should be less than 100 CFU per 100 milliliters. Testing is recommended on an annual basis. (3)

A potential health issue can arise if a cross connection is created between domestic water and rainwater. This can be prevented by installing the make-up water to the cistern with an air gap of at least 2 inches and/or providing a reduced pressure backflow preventer as per the AHJ. Some of the 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. This is like wearing both a belt and suspenders, but if that’s what the AHJ wants, it must be provided – your pants will definitely stay up.

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 non-potable, not for drinking. The labels should be located on piping in walls, within ceiling spaces and on exposed piping.

Recent studies done 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 bacterium 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.5  These studies were done in order to show that no special disinfection measures were necessary for rainwater to be used for non-potable water functions.

In the United States filtration and disinfection of rainwater for potable water use is commonplace.  Several different disinfection processes are used, including:

• Particulate filter(s) with an ultraviolet disinfection unit – the filters must be changed and the UV unit must be cleaned periodically.
• Ozone - 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.

Codes

No national standards exist for the design and installation of rainwater harvesting systems, although some state and local ordinances have been written to address them. Ohio, Kentucky, Hawaii, Arizona, New Mexico, Washington, West Virginia, Texas, and the United States Virgin Islands are a few of the jurisdictions who 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 and International Plumbing Code

Neither the UPC nor the IPC addresses 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 ) states “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 gives 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 (4) may be helpful when planning and preparing for the approval process of AMMR.

• Start early. Identify as many of the non-standard aspects of the project as early as possible.

• Gather information about the jurisdiction and applicable codes. Familiarize yourself 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.

• Find and enlist the help of allies and sources of expertise. 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 with others who have had similar experiences. 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 in 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.

Conclusion

As water shortages become more prevalent in the United States, 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.

References

1. Raincatcher, Funding Provided by State Energy Office North Carolina
2. http://ces.iisc.ernet.in/energy/water/paper/drinkingwater/rainwater/introduction.html
3. Rainwater Harvesting Potential and Guidelines for Texas by Texas Water Development Board, November 2006
4. Checklist for Gaining Approval for Alternative Designs, Materials and Methods of Construction, Environmental Building News, September 2001
5. The Rainwater Technology Handbook by Klaus W. Kong
6. The Texas Manual on Rainwater Harvesting, 3rd Edition, Texas Water Development Board