United States
                       Environmental Protection
                       Office of Water
                       Washington, D.C.
EPA 832-F-00-047
September 2000
Waste water
Technology  Fact  Sheet
High-Efficiency  Toilets

In 1992, Congress passed legislation requiring that
all toilets sold in the United States meet a new
water conservation standard of 1.6 gallons per flush
(gpf). By 1992, in response to the growing need for
conservation of drinking water supply resources,  a
number of metropolitan regions and 17 states had
already instituted water conservation programs
which included high-efficiency toilet requirements.

A national water use standard for a high-efficiency
toilet was necessary to address the problems with
different states and communities having established
different toilet water use standards.  A national
standard eliminated the need for plumbing fixture
firms to manufacture, stock,  and deliver different
products,  and the difficulty for states in preventing
the importation of high-water-use fixtures.

High efficiency designs have significantly improved
since they were  first introduced.   Despite the
improvements, the industry continues to refine this
technology.   Based  on consumer  surveys, the
majority of users are satisfied with the performance
of the current designs.

Because toilets use is the largest proportion of
indoor water used in a household, high-efficiency
toilets achieve real water savings.

The national high-efficiency toilet standard brings
a range of questions and concerns for.  This fact
sheet  is  intended to assist in answering the
questions  that the consumer, property manager,
plumbing  contractor,  and utility  manager might
have about the high-efficiency toilet standards.
                      ENVIRONMENTAL, PUBLIC, AND
                      CONSUMER BENEFITS

                      Studies indicate that converting to water efficient
                      toilets,  showers and clothes washers, results in a
                      household water savings of about 30% compared to
                      conventional fixtures. A change to high-efficiency
                      toilets alone, reduces toilet water use by over 50%
                      and indoor water use by an average of 16%. This
                      translates into a savings of 15,000 to 20,000 gallons
                      per year for a family of four.  Furthermore, more
                      efficient plumbing  products  result  in  lower
                      wastewater flow and increase the available capacity
                      of sewage treatment plants and onsite wastewater
                      disposal systems.

                      The general public also benefits directly from water
                      conservation measures. Practiced on a wide basis,
                      efficient use of water resources helps reduce the
                      potential need during drought periods for water
                      restrictions  such as bans on lawn watering and
                      car-washing. Savings to the consumer from lower
                      water bills, depending on  local water rates and
                      actual use, can range from $50 to $100 per year.
                      Many hotels,  motels,  and office  buildings are
                      finding that new fixtures are saving them 20 percent
                      on water and wastewater costs.


                      The principles of high-efficiency toilet design and
                      operation reflect the shift from remvoing waste by
                      using flushwater volume  to increasing flushwater
                      velocity to remove waste.

                      The  design of the bowl contour became more
                      vertical design to achieve the necessary increased
                      downward velocity. Nevertheless, the bowl contour
                      must ensure a shallow but large water surface

towards the front of the bowl for adequate waste
immersion.     Many  consumers   notice   that
high-efficiency bowl designs result in a flush that
tends to swirl less than their previous toilet.  This
is  because the drag, or friction,  resulting  from
swirling water reduces the essential velocity.

Some manufacturers use an  enhanced front jet
towards the bottom of the bowl to assist in waste
removal.  But other toilets that have received top
consumer survey ratings use no jet at the bottom.

Gravity-flow or pressure-assisted?

Two types of technology are available for both
residential and commercial uses.  The most widely
available is  a high-efficiency modification of the
conventional gravity flow toilet.   The other, the
pressure-assisted toilet, utilizes pressurized air  in
the tank to achieve additional  force.

The choice between gravity and pressurized toilets
usually  hinges  on  two  factors:  noise, and the
distinction between  whether  the maintenance  is
provided  by the homeowner or by a building
manager.  Pressure-assisted toilets are much less
likely to clog than even the older, 3.5 gpf gravity
toilets. While many of the more recent models of
high-efficiency gravity toilets perform as well  as
pressure-assisted  models in  tests,  maintenance
issues for heavy-duty  use,  or responsibility  for
maintaining  multiple toilets,  may  lead  to the
decision to install pressure-assisted toilets.  Some
states, such as New Jersey, require pressure-assisted
toilets in commercial use.

Gravity  toilets  in buildings with cast-iron waste
lines may clog  more  readily,  because  of the
roughness  of the  interior of the  pipe.    New
buildings use PVC pipe, through which waste flows
more easily. Choosing pressure-assisted toilets for
buildings  served  by cast-iron  pipe  may  reduce
maintenance needs.

However, the greater noise from pressure-assisted
toilets is a factor to consider when locating toilets
near sleeping  or  working  quarters. And the
pressure-assisted toilet is generally more costly than
Gravity-flow toilets achieve the necessary enhanced
water   velocity  largely   through  coordinated
improvements of the  siphoning  features of the
fixture.  Indeed, some of the early experiences with
high-efficiency toilets that clogged too easily were
the result of designs that  increased siphoning by
choking down on the trap size.   Manufacturers
responded by re-sizing the trap diameter nearer its
original dimensions,  and instead are coordinating
the rim dimensions, bowl contour, and trap size to
work in concert to enhance the force of the water
and the siphoning function.

Pipe slope standards

The issue has been raised as to whether existing
pipe slope standards are adequate to carry  these
reduced flows.  American Society of Mechanical
Engineers (ASME) tests indicate that the existing
standards exceed performance requirements for
drainline carry minimums.  Field  studies similarly
report very few complaints, representing problems
with a few individual buildings. The standards are
under constant review, and any changes indicated
would   be  recommended  through  normal


Consumer surveys, performed by utilities that have
been implementing high-efficiency toilet programs
(such as rebates), have shown that the vast majority
of 1.6 GPF, high-efficiency toilets work well. For
example, 90 percent of San Diego, CA, customers,
and 95 percent of Austin, TX, customers reported
that they were "satisfied" or "very satisfied" with
their high-efficiency  toilets; 91 percent of Tampa,
FL, ratepayers  said they would purchase the 1.6
gallon   toilet  again.   A  review  of  multiple
metropolitan area customer satisfaction surveys for
the  1995-1998  period   shows   that,   while
performance among  individual   high-efficiency
toilet models varied, the large majority were rated
at least satisfactory in performance, with most rated
better than satisfactory.

Some brands and models have drawn more positive
responses from consumers than others, with specific
models being withdrawn and added as research and
design progress. Since 1992, when the national law

was  first  passed, plumbing products have  gone
through several cycles of improvements, with each
new  generation  bringing  improved   product
performance  and  customer acceptance.    The
marketplace has responded to the move to the
high-efficiency toilet standard so as to better  serve
customer requirements.

The two complaints most often made against the
high-efficiency fixture are somewhat more frequent
clogging, and the perceived need for more frequent
double-flushing. A 1996 survey in New York City
on  customer satisfaction  reported  that  building
managers—who are  responsible for maintaining a
number of toilets-reported more frequent clogging,
probably due to the smaller trap size of the  toilet
(designed   to   increase   siphoning).      The
high-efficiency  toilet designs, as discussed in the
section  on  operation  and  maintenance, cannot
accommodate  extraneous  waste  materials  and
non-flushables  such  as paper towels.   Building
managers should communicate this to their tenants.

In a study of  100  homes in each  of 12 North
American cities, the incidence of double-flushing
was  virtually the same  for homes  with  high-
efficiency toilets as for those with  conventional


The consumer choice of a particular high-efficiency
toilet model must take into account the specifics of
the application.  Key considerations include:

•      To  be sure the new toilet will cover the
       area, check the dimensions of the  space in
       which the toilet is to be installed, including
       the 'footprint' of the old toilet.

       If the drainlines are made of cast-iron rather
       than PVC pipe, the toilet may  be  more
       likely   to   clog.     Ensure  adequate
       maintenance, or consider a pressure-assisted

       Pressure-assisted models tend to  be  more
       noisy  than gravity-flush,  so use  caution
       when installing  this  type  adjacent to
       sleeping quarters.
       Ensure  the  availability of electricity  for
       electric-assisted models.

•      Some toilets have a taller seat height, which
       should be evaluated based on anticipated
       users (some higher  seats  will  be  less
       accessible to children).

•      Users in areas with high mineral content in
       the  water   should   check  rim  hole
       dimensions,  or consider a toilet  with a
       holeless rim.


Purchase:  The buyer of the high-efficiency toilet
should  carry  out  the  same  type  of research
necessary for any significant purchase intended to
be used for a long time.  Refer to current issues of
consumer magazines that evaluate water-efficient
toilets (frequently under article listings  for water
conservation  fixtures).    Your  water  utility,
individual plumbers, and the local plumbers' union
or association  may  also be  able to recommend
certain  models.      Look  for  manufacturers'
guarantees.  By following these tips, purchasers of
water conservation toilets can be fairly assured of
getting a satisfactory product.

Installation:    Proper installation  is  especially
important for high-efficiency toilets.   Licensed
plumbers who guarantee their work will make sure
fixtures are installed correctly.  It is very important
to follow the manufacturer's instructions.   The
proper  flow cycle  for  high-efficiency  toilets is
shorter—usually about 45  seconds—than previous

If installing a water-conserving toilet to replace an
old one, use new mounting bolts of the proper
length, and be sure the old wax seal is completely
removed before installing the new one. Check and
clear drain lines while accessibility is open.

Operation and Maintenance:  The common advice
"Don't use your toilet as a trash bin" is especially
important. High-efficiency toilets will not perform
well if non-flushables, such as paper towels,  are
sent down the fixture.   There has always been a
need for plungers and plumbing "snakes," and their

use  should  be considered first when the toilet
overflows or does not refill completely.

Since flapper valves require replacement  about
every five years,  proper selection of replacement
valves is a key maintenance consideration. A study
conducted by the Metropolitan Water District of
Southern California found that proper flapper valve
model  selection  is  essential  for  continued
performance.  Of  the  physically   compatible
replacement flapper valves, half the models left a
toilet with less  than 1.6  gpf—and the  resulting
incomplete flush had insufficient water to do the
job the toilet was designed to do.  Since most
hardware stores can stock only a few brands, there
is no guarantee of compatibility.  Industry  standards
groups  are  working to insure  that  after-market
flappers will perform properly.  Getting the right
replacement flapper value is worth the effort.

A key problem affecting 1.6 gpf toilets is a result of
the use of chemical in-tank toilet cleaners.  All U.S.
toilet manufacturers recommend against the use of
chemical in-tank toilet cleaners,  as the strong
chemicals degrade  the works  within the  toilet.
Even   with  current  toilets   that   include
chemical-resistant materials, chemical cleaners still
increase the  specific gravity of water and slow
flushing velocity, interfering with performance.

NOTE: Most major toilet manufacturers maintain
1-800 number  Consumer  Hotlines  (call  the
distributor or 1-800-555-1212).  These hotlines are
set up to address both non-technical and technical
questions  relating to installation,  operation,  and
maintenance of high-efficiency toilets.


A wide range of toilets  that  perform  well are
available  in  all   price  ranges,   although  very
inexpensive (less than $100) imports may not carry
the American National  Standards Institute (ANSI)
design  standard  (different  from   the   water
conservation 1.6  gpf standard) and  not function
properly.  In most cases, there is little relationship
between price and performance.   The consumer
choice  recommendations  listed  above   under
"Limitations" will help customers select the right
model for them.
The choice to retrofit based on cost recovery from
water savings can be easily calculated at the local
level based on water rates and the price of the toilet.
For average water/sewer rates, household savings
for a  typical  four-person  household is  about


Other Related Fact Sheets

Other  EPA Fact  Sheets  can be  found  at  the
following web address:


1.      Austin, TX "Common Questions and
       Answers about 1.6 gpf Toilets." Internet
       site at:

2.      Consumers Digest,  July/August:  51-52;
       Geary,  D., 1997. Low-Flush Toilets.

3.      Consumer Reports, "Low-Flow Toilets".
       February, 1995: 121-124.

4.      Consumer Reports, "In Search of a Better
       Toilet."      Internet   site    at

5.      DeOreo, W.B., P.W. Mayer, and P. Lander.
       Evaluating  Conservation Retrofit  Savings
       With Precise End-Use Data.  1998 Annual
       Conference, Water Resources, Vol. B - (2 of
       5 Volumes) June 21-25, 1998, pp. 479-505,
       Dallas, Texas

6.      Koeller, J. M., W.P. McDonnell, and H.O.
       Webster, III. After-Market Replacement of
       Flush Valve Flappers in Ultra-Low-Flush
       Toilets: A Study of Compatibility and Flush

7.     National Trade Association of Plumbing
      Products Manufacturers, April 1998.  Press
      Release.    Report   Credits  Low-Flow
      Plumbing Products with Saving Water and
      Satisfying Customers. Glen Ellyn, Illinois.
                                                The  mention  of trade  names  or commercial
                                                products does  not  constitute  endorsement  or
                                                recommendation for use by the U.S. Environmental
                                                Protection Agency.
      Nelson, J.O., N. Orrett, and J. Weber.  A
      "Choice" ULF Toilet Replacement Strategy.
      1996 Annual Conference, Water Resources,
      June 23-27, 1996, pp. 175-197,  Toronto,
      Ontario, Canada.
       Osann, E.R. and I.E. Young.  April  1988.
       Saving  Water,  Saving Dollars:  Efficient
       Plumbing Products and the Protection of
       America 's Waters. Prepared for American
       Council for an Energy-Efficient Economy,
       Washington, D.C.

       Peak International, April 1996. Ultra Low
       Flush   Toilet   Program,   Customer
       Satisfaction  Surveys.  Prepared  for  the
       Metropolitan Water District  of  Southern
11.     Plumbing-Heating-Cooling   Contractors
       (PHCC) -  National  Association.  1996.
       "Water  Conservation".    Falls  Church,

12.     Swaffield, J.A. and L.S. Galowin.  "Solid
       Waste  Transport  Design  Requirements.
       Design Engineering  Charts for Drainage
       System Pipe Sizing".  Research Proposal to
       the   American   Society   of  Plumbing
       Engineers Research Foundation.  Heriot-
       Watt University, Edinburgh, Scotland.

13.     Water Resources, 1998 Annual Conference,
       Vol. B - (2 of 5 Volumes) June 21-25, 1998,
       pp. 165-173, Dallas, Texas.

14.     Wirthlin Group, October 1995. A Survey of
       Ultra-Low-Flush Toilet Users. Prepared for
       The Los Angeles Department of Water and
                                                        For more information contact:

                                                        Municipal Technology Branch
                                                        U.S. EPA
                                                        Mail Code 4204
                                                        1200 Pennsylvania Ave., NW
                                                        Washington, D.C., 20460
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