Residential Shower and Bath Introduction
The question is often asked: What uses more water, a shower or a bath? The answer has been and always will be, “It all depends …… ”.
Showers are typically the third largest water use in the residential setting after toilets and clothes washers. (As you can see in Figure 1, only toilets and clothes washers are larger.)
According to the the same 1999 study, the average American shower uses 17.2 gallons (65 L) and lasts for 8.2 minutes at an average flow rate of 2.1 gpm (7.9 Lpm) (Mayer, et. al, 1999).
Consumers' Bathing Method and Water Usage
Consumers' Bathroom Habits
How do consumers use their bathrooms in their homes? What are their common habits? In 2008, American Standard performed a bathroom habits survey that provided some very interesting findings.
Market Trends in Residential Showerheads (2005)
This short document provides selected quotations from various interior design trade publications on the topic of the "shower experience". The reader must recognize that these trade publications and their articles are directed at the market for major remodeling and new construction projects. The terms used by the authors of the various statements may, to some extent, exaggerate the significance of these trends.
Water Consumption in the Shower
Two factors influence the water usage of a shower: flow rate and duration. The national Energy Policy Act of 1992 (EPAct 92) standards sets a maximum flow rate of 2.5 gpm (9.5 Lpm) for showerheads manufactured, sold, and/or installed in the U.S. However, there are non-compliant showerheads and shower systems sold in the North American marketplace that exceed this flow rate. Other showerheads are available that use 1.5 gpm or less (5.7 Lpm).
Before 1980, many showerheads exceeded 5 gpm (19 Lpm). Energy conservation initiatives promoted regulations to limit shower flows to reduce hot water usage and the natural gas and electricity used to heat that water. In the mid-1980s, some states restricted showerhead flows to 3.5 gpm (13Lpm), and later reduced further to 3.0 gpm (11 Lpm). The Federal EPAct set a national showerhead flow rate maximum at 2.5 gpm (9.5 Lpm), preempting all state regulations on showerhead flow rates. (NOTE: On December 22, 2010, the U.S. Department of Energy announced that Federal pre-emption of the states as to showerheads and other plumbing products has been waived. This means that states and local jurisdictions in the U.S. are now free to set their own showerhead performance requirements.)
The duration of the shower has an equal effect on water usage. Many have hypothesized reducing flow rates of showerheads might cause users to take much longer showers. Scientific studies that monitored hundreds of homes across the nation have shown that flow rates have little influence on the duration of the shower. In fact, comprehensive studies by Aquacraft, Inc. show that shower duration decreased when more efficient showerheads were installed. The following table summarizes the findings from the East Bay Municipal Utility District service area. The full report contains data from Tampa and Seattle as well (link below).
Average showerhead flow rate
2.0 gpm (7.6 Lpm)
1.81 gpm (6.9 Lpm)
Average shower duration
Source: (Aquacraft, 2005. Water and Energy Savings from High-Efficiency Fixtures and Appliances in Single Family Homes, page 44-45)
Learn more about showerhead flow restrictors and timer devices here:
WaterSense for Showerheads
In 2006, the U.S. Environmental Protection Agency launched WaterSense, its voluntary partnership program. In 2009, WaterSense released its draft specification for residential showerheads. Certification of showerheads and earning the WaterSense label requires conformance with a rigorous set of performance requirements. Those requirements are detailed in the WaterSense showerhead specification and include three significant elements: (1) a ‘force’ requirement sufficient to wash soap and conditioner out of the hair, (2) a ‘coverage’ requirement that ensures wetting of one’s body, and (3) a ‘flow’ requirement not to exceed 2.0 gpm (7.6 Lpm). A more complete discussion of the specification and its background, go here.
The size of the bathtub, and the level to which the user fills the tub affect water use. With the exception of whirlpool and jetted tubs, the size of standard bathtubs in North America has generally decreased over time. The typical modern (non-jetted) bathtub today holds about 25 to 45 gallons (100 to 170 litres) of water depending upon the fill level. While a bather who fills the tub half-way will consume about 20 gallons (75litres), bathers that fill the tub up to (or exceeding) the overflow outlet will use 40 to 50 gallons (150 to 200 litres).
Showers vs. Baths
The response to the opening question can best be illustrated in the following chart.
* Shower spa consumption includes the water usage of the soap/shampoo shower required after the spa event.
As the chart illustrates, a person that takes long showers or uses a high flow rate showerhead can conserve water by using a shallow bath instead. In most cases, but not all, showering is more water efficient than using a bathtub under typical circumstances.
While bathtub water usage is indifferent to duration of the event, water usage from showers is greatly influenced by durations. It is important to eliminate other activities when showering. For example, shaving while in the shower can double or triple the amount of water used. These activities are better managed while taking a bath, rather than a shower because the bath water usage remains constant. .
"Navy Showers" and Lathering Valves
An additional method to reduce water use in showers is to turn off the water while lathering and shampooing, often called a “navy shower”. The method requires three steps: 1) turn on water to rinse body and hair; 2) turn off water while shampooing hair and washing body with soap and washcloth; 3) resume water flow and rinse off all shampoo and soap.
Using this technique, the total duration water flow can be reduced to 5 minutes or less. This is more easily performed when an on-off or lathering valve is attached to the showerhead so the water temperature remains properly adjusted at the desired level. Many water efficient showerheads have integral shut-off valves already attached. Separate “shut-off” or “lathering” valves can be purchased at many hardware stores, and are easily installed between the shower neck and the showerhead. Many organizations (including manufacturers) promote the installation of these showerheads.
Dangers of Thermal Shock and Scalding
CAUTION: While such a lathering valve appears to enable the user to save water, not all homes can use the device. In some cases, it also might endanger that user and lead to thermal shock and/or scalding when the water flow is resumed. In households where the water pressure on the cold water side differs from that on the hot water side (most often where a hot water re-circulating pump exists), closing this small valve could result in hot water flowing into the cold water leg or vice-versa. Depending upon the length of time the valve is closed and the variance in line pressures, when the valve is opened, the temperature of the water exiting the showerhead can be significantly different than it was prior to closure. This sudden temperature shift results in a shock to the body (potentially causing a slip and fall) and possibly scalding in those instances where hot water has backed into the cold water line. For these reasons, showerheads with integral shut-off valves or separate valves designed to be installed between the shower arm and the showerhead are not recommended in the following cases: (1) pre-1987 homes where no scald protection valve is installed behind the wall; (2) showers with flow rates below 2.0 gallons per minute (7.6 Lpm); and (3) showers that are used by elderly or infirm people more easily subject to thermal shock, slipping and falling.
For more information on the hazards associated with scalding and thermal shock in the shower, read this white paper by the American Society of Sanitary Engineers.
Read this warning statement now being attached to plumbing and green building codes and standards in North America.
Read this article in Home Energy Magazine regarding the topic of scalding and thermal shock.
Read this very descriptive article on automatic compensating valves in Plumbing Engineer magazine.
Shower Spray Types
Most showerheads are designed to produce a water spray in one of three major categories: a) stream spray; b) atomizing spray; or, c) aerating spray. Individual preferences determine user satisfaction among the different types of spray. Each type has advantages and disadvantages.
Stream spray showerheads emit the water in many (often more than 20) small continuous streams, and the streams are set in a circular pattern to balance coverage area and comfort. Most users find the water temperature remains fairly constant, but the velocity of the water emitted is somewhat hampered by the need to retain water flow below 2.5 gpm (9.5 Lpm).
Atomizing showerheads use the turbulence of the water passing through the head to create water droplets, and emitting these droplets at high velocity. Most users find the high velocity of the water to be pleasantly invigorating and assisting the rinsing of shampoo from thick hair. The spray pattern is circular, and more filled-in compared to stream spray heads. The disadvantage is the small water droplets tend to cool down quickly as they pass through the air. Some users complain of the water spray feeling hot on their shoulders while cold on their lower legs. This cooling effect also caused an updraft of air in the shower stall, which causes billowing of shower curtains during the shower. Atomizing spray heads were very popular with utility conservation programs in the 1980s and 90s, partially due to the low cost of manufacturing. Advancements in alternate designs and concerns for customer satisfaction has made these models less popular.
Aerating showerheads are very similar to atomizing models, with the addition of air mixed in with the water inside the head through venturi action. The aeration assists in the water appearing more voluminous to the shower user. Unfortunately, the aeration increases the heat transfer of the water, cooling the water faster than even the atomizing spray.
Newer showerhead designs employ multiple sprays types to take advantage of the beneficial aspects of each type of head. These “hybrid” showerheads have resulted in greater consumer satisfaction and water savings. A utility planning to implement a showerhead replacement program should choose products very carefully. Dissatisfied users will remove the showerhead, or tamper with the flow controls; resulting in no water savings. Only the showerheads that remain installed and used will save water for the utility and customer.
With rare exception, re-circulating showers are not designed or operate in a water efficient manner. These systems are often called “vertical body spas” and they often use more water than a typical shower or bath. The re-circulation pumps require a reservoir of water in the shower basin to properly operate. Some makes and models of these systems require more than 45 gallons (170 litres) of water in the basin – more than twice the water usage of a typical shower. The user cannot use any soap or shampoo during the system operation; the spray heads would start emitting suds at a very high velocity and may also clog the head. The user must take a “real” shower after the re-circulating shower, adding additional water usage to the event.
Negative Trends in Residential Systems
Two trends are troubling to water efficiency advocates in North America:
Multiple Showerheads in a Single Stall
There is a growing trend to install multiple showerhead systems in single user shower stalls (compartments) in homes. While not illegal, such systems subvert the intent of the Federal maximum of 2.5 gpm (9.5 Lpm) flow rate for showerheads as contained within EPAct 92.
Fortunately, nearly all of the North American green codes and standards are addressing the multiple showerhead issue by defining the size of a showering stall and next specifying the maximum cumulative flow of all the showers and other water emitters within the stall. Water efficiency advocates are encouraged to support efforts to restrict showerhead installations to no more than one showerhead per 1,800 square inches (1.2 square meters) of shower stall floor area, and require showerheads to be at least 36 inches apart (0.9 meters). This proposed requirement would not allow a second showerhead to be installed unless the shower stall size exceeded 1,800 square inches (1.2 square meters).
Besides multiple showerhead systems, another area of recent and significant concern by water efficiency advocates is the sale of EPAct-non-compliant showerheads over the internet and in U.S.-located kitchen and bath showrooms. Numerous blatant violations of EPAct 92 were disclosed to the U.S. Department of Energy (DOE) by water providers and the Plumbing Manufacturers Institute (PMI) in December 2005. Non-compliant showerheads (with advertised and actual flow rates of 10 gpm (38 Lpm) and greater) and test reports from an accredited laboratory were furnished to the DOE by the PMI in accordance with the DOE process. The DOE did not act upon these violations until 2010. As a result, non-compliant showerheads entered the chain of commerce and were sold to consumers for 4 additional years without any action by the authorities.
In 2010, the DOE belatedly began enforcement actions against a number of manufacturers in non-compliance with the law.
Peter Gleick, President of the Pacific Institute, summarized his opinions on the "Water Scofflaws" (manufacturers offering non-compliant products) and the DOE actions in 2010.
Lawrence Berkeley National Laboratory Showerhead Studies
Sponsored by Seattle Public Utilities, LBNL undertook to assess the impact upon residential water use of non-compliant and multiple-head shower systems. This study was a broad overview of the possible market penetration of such systems, the likely water consumption, and measures that might be taken to reduce water use in residential showers.
Biermayer, P. (2006) Potential Water and Energy Savings from Showerheads
Biermayer, P. (2005) Showerheads - Current Market Trends and Potential Loss of Savings
This presentation, titled "Trends in Shower Design and Their Effect on Energy and Water Use", was given at the ACEEE Summer Study in August 2006. It reflects the findings of the showerhead study listed above as well as additional information on energy and water use.
Biermayer, P. (2006) Trends in Shower Design and Their Effect on Energy and Water Use
2009 - Showerhead study at the University of Waterloo – 12 different showerheads rated by 23 study participants