This research focused primarily on flush efficacy, that is, the ability of water closets to reliably clear waste from the bowl. Most studies did not, however, examine the transport of that waste through drainline systems built using common designs and materials.
Since then, water closet manufacturers have made great strides in improving flushing performance in 1.6 gallons per flush (gpf) (6.0 Liters per flush – Lpf) water closets. Flushing technology has also continued to progress. Many water closet manufacturers are now offering models that further reduce flush volumes to 1.0 gpf (3.8 Lpf) and even 0.8 gpf (3.0 Lpf).
These developments have rightfully raised the debate of drainline carry efficacy anew. Many plumbing experts have questioned whether these reduced flush volumes are approaching a “tipping point” where some sanitary waste systems would be unable to function properly. Of particular concern are larger commercial systems that have long horizontal runs to the sewer. Some drainline transport problems in Europe and Australia have been reported, further raising concerns.
Reduced consumption from water closets is only one contributor to the significant decrease in liquids discharged to building drainlines. Instead, this change has been brought about as a result of reduced indoor water use by many water-consuming devices and equipment. Table 1 in Section 2 illustrates the reductions implemented over the past decades that are now leading to concerns over the function of gravity drainlines. Given these changes, and ongoing efforts to further reduce water consumption, the need to better understand the function of drainlines, as currently constructed, becomes clear. Future reductions in discharges to sanitary plumbing system flows should only be made within the context of a better understanding of how these systems perform and which controllable variables truly impact performance.
Formation of PERC - In an effort to meet the critical need for information on this topic, the Plumbing Efficiency Research Coalition (PERC) was formed. On January 5, 2009, at the U.S. EPA offices in Washington DC, a Memorandum of Understanding (MoU) was executed among five prominent plumbing and water efficiency associations constituting PERC:
- Alliance for Water Efficiency (AWE)
- International Association of Plumbing and Mechanical Officials (IAPMO)
- International Code Council (ICC)
- Plumbing Heating and Cooling Contractors – National Association (PHCC)
- Plumbing Manufacturers International (PMI)
In 2011, the American Society of Plumbing Engineers (ASPE) joined the coalition as its sixth member.
Drainline Testing Priority - The MoU calls for these organizations to collaborate and provide technical expertise towards the development and completion of research programs that foster increased water efficiency in the built environment. The Coalition identified drainline transport of waste in commercial applications as the high-priority, first project to be studied.
PERC then secured the required funding from a wide range of contributors throughout the industry and the country. Additionally, American Standard Brands generously provided both the space and facilities required for the testing program at their Product Development Center located in Piscataway, NJ. Testing commenced on March 12, 2012 and concluded on July 11, 2012.
Past Research on Drainline Transport - Research on the characteristics of waste transport in building drainlines has a history of several decades. The PERC Technical Committee (TC) reviewed a large number of published reports resulting from this earlier research.
In addition, immediately prior to the formation of the PERC in 2009, a “Dry Drains Forum” was convened as part of the ISH trade show in Frankfurt, Germany. At this forum, several prominent researchers and other industry experts provided further information on the causes and effects of ‘starving’ drainlines of liquid flows. Later, other papers and presentations on the topic were discussed at the 2009 CIBW062 conference convened in Düsseldorf, Germany. PERC was represented at both venues.
ASFlow Relationship - ASFlow is an Australian coalition of manufacturers and utility stakeholders that have joined forces specifically to investigate the effect of reduced flows in building drains and sewers. In December of 2010, ASFlow and PERC executed a MoU at U.S. EPA headquarters in Washington, DC. The MoU calls for both organizations to work cooperatively in the development of research initiatives pertaining to the impact of reduced flows on drainline transport.
In the recent past, ASFlow conducted several widely acclaimed research projects, including studies on the impacts of non-water consuming urinals on drainlines, the effect of various horizontal junction fitting designs and associated installation techniques on drainline transport, and the effect of various types of toilet paper on drainline transport. Each of these projects provided needed information on drainline function. Of immediate and significant interest to PERC were the finding related to toilet paper.
Toilet Paper as an Important Variable - In a study by Dr. Steve Cummings, Research and Development Manager, Caroma Dorf, and manufacturer co-chair of the ASFlow committee, the results revealed that selection of toilet paper (and its wet tensile strength) had a profound impact on drainline transport distances. That is, higher strength paper resulted in shorter transport distances. As a result of ASFlow findings, a simple test was developed by the PERC TC to roughly measure the wet tensile strength of toilet paper available in North America. The wet tensile strength test was then used to select a high tensile strength toilet paper for use as a “worst case” selection for the PERC Test Plan.
