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Every three years, there are code change cycles for all the model plumbing code organizations. For the last few decades, there have been water and energy conservation code change proposals that are intended to reduce energy and water consumption levels for plumbing fixtures. During the more recent rounds of code change hearings, the water conservation proposals have seen some success restricting water flow rates beyond the requirements in the Energy Policy Act. I’m all for saving water, but I believe we need to save water by being smart. We need to keep health, safety and system performance in mind. Water conservation efforts are making drainline transport issues and sewer back-ups become more common. This has led to a phenomenon known as “Dry Drains.”
I had the honor of being asked to be one of the speakers at a Dry Drains Forum a few years ago. The forum was held in conjunction with the International Sanitation and Heating (ISH) conference and expo in Frankfurt, Germany, and hosted speakers from around the world who gave presentations about drainline transport issues they were facing in their countries. The speakers realized that they were dealing with similar issues related to water conservation efforts in their respective countries causing drainline transport issues. We are reaching a point in water conservation efforts where there is not enough water left in the drain to transport solids. I have often said, “there needs to be enough water left in the river to float the boats.” This is becoming more and more obvious in states like California and Texas, where they are exceeding the mandated energy and water conservation limits in the Energy Policy Act of 1992. The number of sewer cleaning calls has gone up significantly in these areas where water conservation efforts are more aggressive. This is good news if you own a drain cleaning business, but it is not good news if you are a homeowner or a building owner or tenant in a building experiencing problems.
Energy and water savings mandates are contributing to dry drains
There will always be fresh water because fresh water is constantly circulating in the hydrological cycle — evaporating, condensing into rain, falling to earth, and flowing into the streams, lakes and the ground as groundwater. The rainwater flows into the ocean where it mixes with salt water. We can catch the rainwater in tanks and hold the rainwater run-off in reservoirs for treatment and use it as fresh/potable water.
We also have the technology to convert seawater into fresh water with reverse osmosis systems. The key for us is to learn how to manage the fresh water resources and development so that development does not outpace the ability to provide fresh water in arid regions.
In many cases, proper engineering and planning can provide additional reservoir capacity to store more fresh water, which would require acquiring land for the reservoir, the dam, the treatment facilities, the pumping stations and water mains.
The United Nations conducted a study on the total amount of water in the world and it gave a breakdown of the freshwater resources. The study shows that 97.5 percent of the Earth’s water is salt water and only 2.5 percent is fresh water. The study went on to show about 70 percent of the fresh water is trapped in ice and snow in glaciers in mountainous regions and polar ice caps. About 29.7 percent or 30 percent of the fresh water is in groundwater, and the remaining 0.3 percent is available to us in the form of fresh surface water in rivers, lakes and streams.
Total world water and breakdown of freshwater resources. (Note: Numbers are rounded, so percent summations may not equal 100.
Source: Igor Shiklomanov's chapter "World fresh water resources" in Peter H. Gleick (editor), 1993, Water in Crisis: A Guide to the World's Fresh Water Resources (Oxford University Press, New York).
Water uses in the U.S.
According to a U.S. Geological Survey conducted by the EPA, 87 percent of the fresh water use in the U.S. is for non-residential water use. Non-Residential users include agricultural, industrial and commercial uses.
Large water users include the industries that produce metals, wood and paper products, chemicals, gasoline and oils. Just about every manufactured product uses water during some part of the production process. Other industrial water uses include water used for such purposes as washing, diluting, cooling, or transporting a product. Some uses incorporate water into a product, or water may be used with disinfection chemicals for sanitation. Substantial amounts of water are used to wash down equipment, rooms and floors within manufacturing facilities and in food processing, meat packing and dairy processing plants. Other industries that use substantial amounts of water produce such commodities as paper pulp for a variety of uses like diapers, facial tissue, newspapers, and other paper products. Water is used in chemical plants, for condensing towers in refineries and petroleum plants, or for cooling water in primary metal processing plants. Irrigation water use includes water used for growing crops, frost protection, chemical applications, weed control, and other agricultural purposes, as well as irrigation and washdown water used to maintain areas such as parks and golf courses. Other uses include private water wells, livestock, aquaculture, fish hatcheries, and mining activities. Electric power accounts for a significant use of water withdrawals. Most of the water is derived from surface water and used for once-through evaporative cooling at power plants.
Only 8 percent of all water use in the U.S., however, is residential. Yet this is where much of the focus of the federal laws dealing with water conservation have been. I would like to see more focus on conserving water in the other segments discussed above; there is an enormous potential for water savings in these industries.
Facts about water use in the United States.
Source: U.S. Geological Survey, Environmental Protection Agency
If residential water use is reported to be 8 percent of all water use, then 92 percent of all other freshwater use is from non-residential segments. Water and energy conservation code changes have been focusing on saving water for fixtures like: water closets, lavatories, sinks and showers. These efforts to further reduce water use is causing performance issues with respect to drainline transport of solids, as well as other problems. On the other end of the plumbing system, the water conservation is affecting the quality in the water supply system with reduced water usage causing aging water issues.
Aging water occurs when the lower flow rates allow water to linger in the distribution piping for longer periods of time. The water treatment chemicals continue to dissipate at the same rate and they are dissipating down to ineffective levels to control bacteria growth in municipal and building water systems. The significant increase in Legionella outbreaks recorded since the advent of the Energy Policy Act seems to show a correlation in the increase in reported cases of Legionnaires’ disease along with the mandated decrease in plumbing fixture flow rates. There are ongoing studies at Drexel University and Purdue University looking into the effects of water conservation programs on water quality. We should hear about the results of these studies in a few years.
The 1992 Energy Policy Act
In 1992, the federal Energy Policy Act was passed and has since undergoned various amendments. The broad focus of this law is to increase clean energy use and improve overall energy efficiency in the U.S. Mandates for the reduction of water usage by residential and commercial users were included in this law based upon the understanding that the production and distribution of water requires energy. The law sets minimum efficiency standards for flow rates for water closets, urinals, faucets and showerheads, (except emergency fixture showerheads) that are distributed in commerce for personal use or commercial use or consumption.
The minimum efficiency standards for water closets, urinals faucets and showerheads set forth in the 1992 Energy Policy Act, section 123, are covered in Title 42 USC section 6295(j) and, 6295 (k):
There are similar maximum flow requirements for faucets and showers in section (j). These flow rate reductions have led to an increased number of drainline transport problems for older plumbing systems when they were combined with poorly designed and poorly performing plumbing fixtures at the time. Manufacturers had to spend great sums of money to redesign water closets to flush with better performance. We are approaching the point where manufacturers cannot make many more improvements to plumbing fixture performance at these very low flow rates. There is a minimum amount of water required to maintain a hydraulic depth of flow in a drain and for drains to flow and perform properly. When low-flow plumbing fixtures are installed on older plumbing systems that have existing larger drains installed at the minimum slope, the lower flows create a lower hydraulic depth of flow in the drain and solids will not transport down the drain as well. They tend to pile up and form a dam over time. The dam creates a pond in from of the dam where flow velocities are interrupted allowing solids to settle out in the pond that is formed in the drain pipe. Over a period of time, the solids plug up the existing oversized drainlines. This necessitates a call for a drain cleaning service technician.
Many of us may have heard about problems in drains and sewers following the advent of the 1992 Energy Policy Act and the mandated water flow reductions. Since then, the plumbing product manufacturers have invested a lot of money redesigning their fixtures to perform better at lower flows, however there is a limit to the possible improvements with respect to performance. The Plumbing Industry Research Coalition (PERC) was formed and has been doing research to learn more about the drainline transport issues using low-flow fixtures. Its funding has been limited, and more research is needed, to address issues with flushable wipes, flushable toilet seat covers, and feminine products in the drainline. The research it has provided so far has been valuable with respect to understanding the limitations of plumbing fixtures and drain line transport at lower flow rates. Click here for information on the PERC research (Phase 1, Phase 2 and Phase 2.1).
Studies by two engineers, Bill Gauley and John Koeller, show that when various models of 1.6 and 1.28 gallon per flush (GPF) water closets were tested, tests showed drainline transport of solids is generally less in 1.28 GPF water closets when compared to 1.6 GPF water closets. There was a reduction in the drainline transport of about 37 percent when reducing flows from 1.6 to 1.28 GPF. The transport distance was reduced from 36 feet on average to about 23 feet. (See Figure 4) With even lower flows being proposed, it will be difficult, if not impossible, for larger horizontal drainage systems to transport solids. Drain blockages will become more common at lower flow rates. In high-rise vertical buildings, it should be relatively easy to transport the waste a short distance to a vertical stack if the stack is within about 15 feet of the fixtures. There should be enough additional uses of water in the stack in a high-rise building to provide sufficient drainline transport at the lowest level in the horizontal building drain.
In a remote restroom in a large horizontal building, with no other branches providing drainage flow, there will be drainline transport problems and an increase in drainline blockages. The energy expended after cleaning up after a sewage back-up could easily exceed the cost associated with having an adequate drain flow in the original system design. When you consider the energy and expenses associated with cleaning the drain lines; removing moldy drywall and finishes; repairing damage to the building; healthcare costs associated with the spread of disease, bacteria and mold, the small amount of energy and water that may be saved will be offset by far with remediation costs.
Another consideration that I have experienced is, when people realize the drains block-up on a regular basis because of inadequate flow, people will be trained to flush twice or three times to ensure the waste goes down the drain. I have seen signs in many restrooms asking users to flush multiple times if there are solids in the bowl. There is a minimum sustainable drainline flow rate and more research is needed to understand these limitations before we arbitrarily pick lower flow rates in order to gain points for an energy and environmental, water conservation program.
Drainline transport distance at various flow rates.
Source: Evaluation of Low-Flush-Volume Toilet Technologies to Carry Waste in Drainlines, February 2005, by: Bill Gauley, P.Eng., and John Koeller, P.E.
The dry drains phenomenon
Dry drains are a phenomenon being brought about because of aggressive energy and water conservation efforts. Energy and water conservation code changes continue to be proposed for further reductions of water consumption for plumbing fixtures beyond the requirements in the Energy Policy Act of 1992. These water flow reduction proposals are what I have referred to in the past as the “water conservation limbo: how low can we go?” Using the Manning Formula, and from various drainage research that is available, we have a basic understanding of the minimum flow required for each pipe size and pipe slope for various drain loadings. Despite this available knowledge, people still propose code change submittals based on simple math of water savings based on a lower flow over a fixture use period. There is no consideration of the impact on other parts of the plumbing system. Many code change proposals don’t consider the laws of physics. Many code changes seem to be on the edge of violating, or maybe already violating, the laws of physics. However, plumbing systems should perform properly with health and safety being more important than energy and water conservation. The international code change process has an option to click that asks: “Does the proposed code change will add cost to building construction.” I would like to see an option that asks: “Will this code change potentially cause a decrease in system performance?” I would also like to see an option for: “Will this code change cause a health and safety issue?”
Code changes should be provided with technical support and research that shows no adverse effect on system performance, and health and safety issues. The problem is complex and a simple request to save water comes with many other performance and health and safety ramifications that are not always contemplated by code change proponents with the good intentions of saving water.
Drain flows are getting to the point where the flows are insufficient to transport solids down the drain. If drain flows are reduced, and the drain pipes are the same size, then the hydraulic depth of flow will be less. In older buildings, there will likely be more problems than in newer buildings that can be designed with smaller drains with more slope.
To compound the issue, when a greywater reuse system collects discharged water from fixtures for reuse to flush water closets or for sub-surface irrigation purposes, it is taking water away from the sanitary drainage system. (See Figure 4). The wastewater flow needs to be maintained at a level to keep the hydraulic depth of flow sufficient for proper water velocities and drainline transport.
There is less water in drains due to water conservation.
Loss of hydraulic depth in building drains from flow into horizontal branch drains
There has been research done in Australia that was reported on at the Dry Drains Forum that addressed flows in horizontal building drains with horizontal branch connections. The study showed when building drain branches are connected horizontally to the building drain, they allow waste to divert or back-up into each branch as the waste flows by each branch. This lowers the hydraulic depth of flow in the main. (See Figures 5, 6 & 7) This illustrates the need to consider code requirements to roll up branches on a 45-degree angle to prevent the waste from entering the branches (and further reducing the drainline transport capacity for drains that are already at or near minimum flow rates for proper drainline transport for ultra-low flow fixtures).
The research also confirmed a drain should not drop from directly overhead into a horizontal drain. Waste usually would be directed upstream from a vertical stack dropping into a horizontal drain. This allowed solids to settle in the horizontal pipe upstream of the connection and reduce the hydraulic depth of flow because of the diversion of waste. The stack should use a 45 and a Y fitting rolled to allow a rolled up 45-degree entry into the horizontal drain.
Some of these are already required in our codes. We should also be more aware of using directional drainage pattern fittings as water closet flow rates that are further reduced. An interesting thing of note is the fact that the minimum slope in Australia is 1.67 percent, and in the U.S., the minimum slope is 1.0104 percent (1/8 inch per foot) because we generally use smaller drain pipes.
Figure 6 – Less water in drains due to flow into horizontal branch connections.
Figure 7 – Less water in drains due to flow into multiple horizontal branch connections.
Figure 8 – Rolled up branch drain to assist with transport of solids.
Figure 9 – Large pipe with low flow fixtures = low hydraulic depth and drainline transport problems.
Figure 10 – small pipe with low flow fixtures = good hydraulic depth and drainline transport. (Smaller pipes may require increased slope)
As a member of a water utility, we were experiencing water quality problems at the ends of the water distribution network because of aging water. We were also dealing with blockages in the sewer mains because there was not enough flow in the sewers. We ended up flushing fire hydrants every couple of weeks and directing the flow into sewer manholes to address the water quality and drain flushing the sewers. How is this accounted for in the energy and water conservation calculations?
I am hope the water quality studies associated with water conservation programs at Drexel University and Purdue University look at the issue of water and sewer departments needing to flush water mains to maintain water quality at the ends of their water distribution systems. This seems counter-productive, but is necessary for safe drinking water and to flush the poorly performing sewers.
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