The Water Economy of a Low Flush Toilet in a
Water Deficient Region
by
Albert E. Pratt
Water Resources Research Center
Caribbean Research Institute
College of the Virgin Islands
St. Thomas, USVl' 00801
Contract No. A-004-VI
Research Period 3/77 to 9/78
A project completion report.
July 1979
The work upon which this report is based
was supported by funds provided by the United
States Department of the Interior, Office of
Water Research and Technology as authorized
under the Water Resources Act of 1964, P.L. 88-379
Technical Report No. 3
Water Resources Research Center
Caribbean Research Institute
College of the Virgin Islands
St. Thomas, USVI 00801
ABSTRACT
Water use at a public restroom facility was sub
stantially reduced after installation of low-flush
toilets. Water in the region is scarce, demand is
high, and water is expensive. The first year of
operation of the low-flush toilets saved 36,500
gallons and reduced the true cost of water used
at the facility, predominately desalted water, from
$757 to $210. The research demonstrated the prac
tical value of a conservation technique that, if
widely used in the Territory, could substantially
reduce costs for government water and energy pro
duction.
111
CONTENTS £aS£
LIST OF FIGURES VI
LIST OF TABLES vii
INTRODUCTION 1
OBJECTIVES 2
SCOPE 2
APPROACH AND METHODS 2
RESULTS AND DISCUSSION 3
Public School Use 7
Overnight Accommodations Use 8
Government Office Use 8
Public Housing Use 8
Residential Use 8
RECOMMENDATIONS 9
ACKNOWLEDGEMENTS 10
LITERATURE 11
TABLES 12
APPENDIX A 19
LIST OF FIGURES
Page
1. Record of Water Use at Red Hook 4
VI
LIST OF TABLES
Page
1. Water Center Water Meter Records 12
2. Comparison of Water Use Records
for the Red Hook Facility 13
3. Installation of Low-Flush Toilets at Red Hook 14
4. Public Works Department; Jan. 1976-Dec. 1976 15
5. Public Works Department; Jan. 1977-Dec. 1977 16
6. Public Works Department; Jan. 1978-Sept. 1978 17
7. Public Works Department; Oct. 1978-May 1979 18
vn
INTRODUCTION AND OVERVIEW
The Territory of the U.S. Virgin Islands is composed of three main
islands: St. Croix (84 sq. mi.), St. Thomas (28 sq. mi.), and
St. John (20 sq. mi.), and more than 60 smaller islands and cays.
The islands as a group receive an average of 40 inches of rainfall
annually; however, about 90 percent of that rainfall is lost to
evapotranspiration and the group of tropical, oceanic islands is
classified as being semi-arid. The water resources, therefore,
are scarce and generally of poor quality. Because of the limited
scale of each island, there is no hinterland from which to draw
additional resources.
Approximately 100,000 people live on the land area of 135 square
miles. Most of the population relies directly on roof catchment and
cistern storage of the inconstant rainfall for household water sup
plies.
The Territory experienced a period of phenomenal economic growth and
population expansion during the 1960's and 1970's. The government
invested heavily in sea water desalting plants in an attempt to re
lieve the chronic short supply of potable water created by the de
mands of a booming tourism-based economy. Temporarily successful
in fulfilling the needs for potable water, by the mid-70's opera
tional failures of the desalting equipment in combination with a
continual reliance on inefficient and obsolete distribution systems
and the meteorically rising price of energy made it impossible for
the government to meet daily potable water needs, and a six-hour
per day rationing schedule was imposed on public water supplies.
At peak production, the desalting plants are capable of supplying
approximately 75% of the estimated peak daily demand of 5.5 million
gallons of potable water for the Territory. Present cost for de
salting sea water is assumed to be at least $15 per thousand gallons;
the true cost of production for the V.I. Water and Power Authority
is not known. The water is distributed to the public by the Virgin
Islands government (Public Works Department) and consumers are
charged a rate of $4 per thousand gallons, making it necessary for
the government to substantially subsidize Territorial water supply
programs.
Conservation of water has therefore been identified as one of the
ways the Virgin Islands government can reduce the strain of the
present fiscal squeeze.
The Virgin Islands Water Resources Research Center, through a grant
from the U.S. Department of Interior, Office of Water Research and
Technology, installed several low-flush toilets in a heavily trafficked
public restroom facility on St. Thomas and monitored the performance
of those units for a period of seventeen (17) months. The project
served a practical use for the residents and visitors of the Terri
tory and demonstrated the conservation and cost-saving potential of
such equipment to the public agencies that operate and service the
public restroom facility.
OBJECTIVES
The project was intended to measure a reduction in water usage at a
public restroom facility after installation of low-flush toilets,
monitor maintenance and operational problems, and evaluate the net
effects that wide-scale use of low-flush equipment could have on the
present level of demand for government water production and distri
bution.
SCOPE
The installation of low-flush toilets in combination with a monitoring
program provided the opportunity to evaluate the effects of reducing
the amount of water required for sanitary flushing on: a) the daily
water needs for operating a specific restroom facility, b) Territory-
wide water needs by projecting a reduction of demand, and c) reducing
the cost of water for an average household in the U.S. Virgin Islands.
APPROACH AMD METHODS
Five (5) conventional toilets in a public restroom facility at Red
Hook Ferry Dock, St. Thomas were replaced with low-flush units at a
total cost of $3580. The facility is operated by the V.I. Ports
Authority and v/as selected as the project site because it serves the
needs of the many residents of St. John and St. Thomas as v/ell as
tourists who regularly use the St. Thomas-St. John ferries.
Water for the facility is supplied without cost to the Ports Authority
by the Public Works Department. Water is trucked as needed from the
public standpipe in Sub-base, about twelve miles away, and is stored
at the site in a 1,000 gallon steel tank. It is then pumped to the
restroom for use in the lavoratories and for sanitary flushing.
The low-flush units that were installed were Microphor LF-310 stain
less steel toilets. The system requires 50-70 PSI of compressed air
and a small amount of water from gravity flow or, as in this project,
at 1-60 PSI. A push button mounted on the toilet activates a flow of
water into the bowl and opens a valve in the base of the toilet. The
valve is then closed automatically and a charge of compressed air
ejects waste materials into a discharge line.
The Microphor unit is designed to operate on two (2) quarts of water
per flush. All parts of the unit are corrosion resistant, a benefi
cial feature because of the high level of chlorides present in most of
the water delivered to the facility.
A water meter was installed in the feed line between the storage tank
and the restroom.
The newly-completed installation was tested on February 24, 1977.
From 7:30 a.m. until 3:15 p.m. there was a total of 60 flushes of
the units and 30 gallons of water was used. A conventional toilet
would have required more than 300 gallons for the identical use.
Operation of the facility was monitored for a period of seventeen
(17) months, from February 24, 1977 to June 22, 1978. Water delivery
records were submitted for analysis by the Public Works Department
for the period January 1, 1976 to June 30, 1979.
RESULTS AND DISCUSSION
The theoretical reduction of the water used for sanitary flushing at
the Red Hook facility is a factor of at least 10:1. The 10:1 reduc
tion is the result of replacing the conventional flush toilets which
require five (5) gallons (or more) per flush with units that require
only two (2) quarts (or, 0.5 gallons) of water per flush.
In order to test the performance of the retrofitted facility, data
was aggregated by reporting calendar quarters. Four quarters of the
research period were then isolated for which good comparisons of the
data could be made. The analysis period selected was from April 1977
through March 1978.
During the analysis period, the Public Works Department records show
that a total of 14,000 gallons of water was delivered to the Red Hook
facility: a total of 50,500 gallons was delivered for the correspond
ing period one year earlier.
No count was made of the number of people using the facility and no
records of previous levels of use exist. For purposes of this study,
it was assumed that traffic patterns were similar for the years 1976-
1978. (Note: Maintenance personnel noted that there appeared to be
an increase in traffic during the research period, and that it was
probably due to the improvement of the facility.)
FIG. 1 Record of Water Use at Red Hook
PROJECT NO. A-004-VI The Water Economy of a Low-flush Toilet
CALENDAR QUARTERS
18000
16000
14000
12000
o 10000
i—
-
treatment and environmental protection.
Flush Cycle: 12-18 seconds
Water Usage: 2 quarts per flush y a"roa<* com.
Warranty: One year — all parts
Air Use: 1 cubic foot free air at 60 psi
Discharge Line: 11/2 inch pipe size
P.O. Box 490 D Willits, California 95490 • (707) 459-5563
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