Despite the current downturn in residential and commercial construction, interest in green building practices continues to grow. There are several reasons for this. First and foremost, homeowners and property managers want lower utility bills. Second, the past several years have seen an explosion in the number and selection of “green” products, and the increased competition has driven prices downward. Finally, consumers of all types are thinking more about how their choices impact the environment, and want to know what they can do.
Plumbing and mechanical engineers play a key role in helping make a successful transition to more environmentally friendly buildings. It is not enough to specify water or energy-efficient products. Engineers must be able to explain why these products are preferable, how such products will affect the building’s function, and then design systems that provide the benefits of lower operating costs while maintaining the occupants’ safety and comfort.
Water Efficiency in the HomeMany designers are looking to incorporate “green” aspects into projects. Whether designing a new home, or doing a kitchen or bathroom remodel, it’s important to understand how the various subsystems - plumbing, HVAC, electrical, lighting, etc. - need to work together to provide the homeowner with the desired experience.
A holistic look at water efficiency includes consideration of aspects beyond just fixture and faucet water consumption. Some of these aspects include:
Water efficiency will reduce the homeowner’s water and sewer bills. Based on average rates, use of water-efficient plumbing products can save $100-$200 per year in water and sewer charges. Homes that are less expensive to operate often sell for a premium, although energy efficiency is a much larger contributor to this than water efficiency.
More importantly, homes that use less water help their community stretch existing water supplies. While water is plentiful in most areas today, the Environmental Protection Agency expects all or parts of 36 states to be “water stressed” by 2015. By making more efficient use of existing supplies, homeowners can help avert the need to develop new supplies, which are often much more expensive, and reduce the need for more aggressive conservation practices such as sprinkling bans or water rationing.
Residential Water Use PatternsData from the US Geological Survey shows that per capita water use in the United States is about 155 gallons per day. About one-third of that is used in businesses and public spaces, with about two-thirds, or 100 gallons per person per day, used in homes.
To break it down further, approximately 70 gallons per person are used indoors, while 30 gallons are used outdoors for landscape irrigation, car washing, swimming pools, etc. Outdoor use varies widely across the United States - some areas use 10 gallons per person per day, or less, while others use upwards of 200 gallons per person. Variations are primarily due to climate-related differences in landscape water demand.
The Residential End Uses of Water (REUWS) study (DeOreo and Mayer, 1999) identified the Top 5 indoor uses of water in homes as toilets, clothes washers, showers, faucets, and system leaks. Combined, these account for nearly 95% of indoor water use. Studies are currently underway to see whether and how much water use patterns have changed in the past decade.
Be aware that these are averages. Each home will be slightly different, depending on the choices that the residents make regarding water use. Getting people to change behavior has not proven effective for long-term water savings. Instead, use of water-efficient plumbing products and appliances is the easiest and most reliable means of reducing indoor water use.
26.7% of Indoor Water Use
Toilet design has come a long way in the past 15 years. Today’s models are engineered to meet a variety of performance criteria including plug resistance, waste removal, cleanliness, minimal noise, along with reduced water use. Per the Energy Policy Act of 1992 (EPAct 92), toilets cannot use more than 1.6 gallons of water per flush. However, high-efficiency toilets, or “HETs,” have been introduced in the past few years. HETs use at least 20% less water than a standard toilet, or no more than 1.28 gpf. These toilets are subjected to all the same performance testing as standard toilets, and most out-perform old 3.5-gallon toilets.
Many different types of HETs are now available. High-performance gravity toilets, pressure-assisted toilets, commercial flushometers, and dual-flush toilets offer consumers a wide range of choices at different price points. In the case of toilets, there is no need to sacrifice performance or style to save water. When selecting a high-efficiency toilet, look for models that carry EPA’s WaterSenseSM label.
Replacement of pre-1992 toilets in existing homes still represents a significant opportunity for water savings in the United States. Surveys estimate there are still nearly 100 million of these toilets in use, representing more than 1.5 billion gallons per day of potential water savings.
21.7% of Indoor Water Use
Laundry accounts for a significant amount of water use in the average home. Clothes washers have been part of EPA’s Energy Star program for many years, but until 2007 there was no requirement for water efficiency. Starting in July 2009, the Energy Star program now includes a maximum “water factor” of 7.5, which means clothes washers cannot use more than 7.5 gallons per cubic foot of capacity, per cycle. This value will drop to 6.0 in 2011. However, many clothes washers on the market today have water factors of 4.5 or lower. In general, clothes washers with horizontal axis designs are more water efficient than top-loading machines.
16.8% of Indoor Water Use
The next highest user of water in a typical home is the shower. A standard showerhead cannot exceed 2.5 gpm of water flow per EPAct 92. Low-flow showerheads can save thousands of gallons of water per year, but as water flow is decreased it becomes more challenging to provide a satisfactory experience for the user. Product manufacturers are working in conjunction with testing and certification organizations to develop a performance test for showerheads. This test will allow high-performing, water-efficient showerheads to be incorporated into EPA’s WaterSense program. In the meantime, several manufacturers offer multi-function showerheads that work great and still only use 2.0 gpm or less.
A concern among water-efficiency advocates is the growing popularity of showering systems that can deliver substantially more water than a single 2.5-gpm showerhead. Attempts to limit the designs and net potable water use of these systems in green home programs and new building codes are ongoing. While it is clear that such systems consume more water when operated at full capacity, research on how they are typically used is needed to better understand their impact on indoor water use. These systems still represent a small portion of the overall showering market.
15.7% of Indoor Water Use
Faucet aerators are the easiest and least expensive way to save water in a home. Aerators are available for most residential faucets. Faucet aerators that reduce flows from 2.2 gpm to 1.5 gpm or less do not affect one’s ability to wash hands or brush teeth, and only cost a few dollars per faucet to install. If the entire faucet is to be replaced, choose a lavatory faucet certified to carry the WaterSense label. WaterSense faucets use between 0.8 and 1.5 gpm.
Most conservation professionals put less emphasis on reducing flows of kitchen faucets. Water use in the kitchen is primarily volumetric - filling pots or drinking glasses. Reducing flow for these applications will not save water, but will just make them take longer to accomplish. Kitchen faucets should deliver no more than 2.2 gpm.
13.7% of Indoor Water Use
The older the home, the more likely that fixtures, faucets, showerheads, or other water-consuming devices have developed leaks. Repair or replacement of leaks should be a priority in any home, as this represents a significant and unnecessary waste of water and money. Many leak detection kits are commercially available; some are even provided free of charge by local water utilities. Most new fixtures and faucets are engineered to be much more leak-resistant. Toilets that have canister-type valves instead of flapper valves, and faucets that have ceramic disk seats are two examples. Water use audits are helpful in identifying the presence of leaks in existing homes.
Table 1 shows the effects that various water saving devices can have on estimated indoor water use. Use patterns for the EPAct 92-compliant home and water-efficient home are identical to those reported in the Residential End Uses of Water study. Therefore, any savings shown is strictly due to changing the devices and not due to changes in user behavior. Just installing standard devices delivers a water use of 52.1 gpcd, while installing the most water-efficient products available today reduces that to 41.6 gpcd, or 40% less than the average.
Emerging Technologies and Issues in Water EfficiencyAs shown in Table 1, the 40 gpcd home is achievable using existing water-efficient plumbing products and appliances. While it is likely that manufacturers will continue to develop products that use even less water, new systems and technologies will be necessary to reduce overall residential water use further.
Use of graywater is one such technology that is currently drawing attention. Graywater is non-potable water collected from showers, bathtubs, and lavatories. It tends to contain relatively low levels of suspended solids and microorganisms, and is suitable for use in flushing toilets and urinals, given proper treatment and handling. Plumbing codes for graywater are in development. Once these codes become finalized, more of these systems will be installed, especially in arid regions. Caution is warranted, however, as there may be unexpected health and sanitation issues related to storage and handling of graywater.
Of a more long-term concern is whether existing sanitary sewers can function properly with decreased water flows. Reduced water use in homes, combined with sewer replacement that decreases infiltration of groundwater, may have adverse consequences for these systems. It is not clear at what point this will become a problem.
Beyond Water Efficiency to "Green"Water efficiency is just one aspect of a green home. Many consumers are now asking about how products are made and whether they are environmentally friendly. There is no standard definition of a “green” product, which has provided marketers with a lot of leeway to highlight specific product attributes and call them “green.” However, there are general aspects of a product that all should be evaluated. These include:
Transforming the plumbing products market toward water-efficient products that are also “green” will take time, but is occurring today. Building designers, engineers, and plumbers can support this transformation by understanding the impacts of these new technologies and sharing that knowledge with clients and customers.