Measuring Water Conservation Against Performance

For the better part of the last three decades, there has been a growing demand for water conservation and an urgency to drive toilet-flush volumes lower.

But even advancements in water savings don’t come without concerns. Although reducing the water use of plumbing fixtures prompts the emergence of low-flow, high-efficiency toilets that support water conservation, unintentional consequences such as a lack of water pressure and satisfactory bowl performance are negatively affecting drain line function.

When you look at overall water consumption in commercial buildings, restrooms are responsible for a large percentage of that total water use — close to 45% in schools and about 37% in office buildings. As water and sewer rates continue to increase the demand for water conservation, that topic is at the forefront of the sustainability conversation at the design and ownership levels. In fact, the World Economic Forum designated financial failure as the top global risk from 2012–14, before labeling the looming water crisis as its top priority in 2015.

But when it comes to low-flow plumbing fixtures, knowing just how much water to eliminate from the design can be a critical balancing act.

How Low Can You Go?
The conversation around water conservation was brought front and center in the early 1990s, when the Federal Policy Act of 1992 was passed by Congress. It set maximum water consumption standards and reduced water use in plumbing fixtures to 1.6 gallons per flush (gpf) for toilets on a national level. Plumbing manufacturers soon engineered 1.28 gpf flushometers before dropping high-efficiency toilet systems down to 1.1 gpf, ultimately marking a 31% water savings from its original 1.6 gpf predecessor.

Other alternatives, such as waterfree and hybrid urinals and reclaimed water flushometers—designed to preserve potable resources and withstand the harsh conditions reclaimed water presents—followed suit. But as manufacturers continued to innovate with sub-1.1 gpf flush volumes on toilet fixtures, variations in performance were soon discovered.

The PERCs of Plumbing Research
Recognizing the ongoing efforts to make plumbing systems as efficient as possible, the Plumbing Efficiency Research Coalition (PERC I) study sought to apply a scientific approach toward a better understanding of drain line function under lower flow conditions to equip the plumbing industry with the tools to work proactively to prevent widespread blockages from becoming a reality.

The PERC I study found that at the 0.8 gpf flush volume, there was a demonstrated major difference in performance compared to the other volumes tested. In five of the 16 test runs conducted at this low volume, the test media compressed together to form large plugs in the drain line that resulted in full-pipe blockage or near full-pipe blockage conditions.

The 1.28 gpf and 1.6 gpf test runs, on the other hand, resulted in an “orderly and predictable movement in the test apparatus.” The good news is that the 1.1 gpf valve/fixture combinations are likely to mirror the 1.28 gpf and 1.6 gpf flush volumes.

The PERC I study presents results that can be easily implemented in an ideal building environment such as new construction. However, the PERC I study does not address or recognize the larger base of existing buildings and their existing plumbing infrastructure.

When incorporating high-efficiency fixtures in an existing building such as in a retrofit or a remodel, agreater consideration of the existing conditions and capacities of the drainage and supply systems often is required. Anything below 1.28 gpf are circumspect, as there are variables that can negatively impact drain line carry. Flush volumes at or above 1.28 gpf have so far proven themselves in the existing commercial marketplace.

Conservation Counts
Water is an essential natural resource. All the water that is currently on the Earth is all the water that we will ever have. So when you consider that people in developing countries exist on less than three gallons of water per day, while most Americans routinely use that amount to brush their teeth; or that we could save approximately 177 billion gallons per day just by fixing leaking fixtures, it presents the true magnitude of water conservation across the planet.

But despite the need to decrease water consumption, there is a fine balance between both sanitation, efficiency and conservation, as water reduction can only go so far before compromising hygiene and drain-line performance.

About the Author
Patrick Boyle is the director of corporate sustainability at Sloan.