Estimated Per Capita Water Ingestion in the United States
This report provides estimates of per capita water ingestion in
the United States based on the USDA 1994-96 Continuing Survey of
Food Intakes by Individuals (CSFII). Results are presented for
the general population and for cetrain subpopulations including
gender and age categories, pregnant and lactating women. These ingestion
estimates may be used in estimating risk to human health from the
ingestion of contaminated waters. Knowledge of water ingestion is
of fundamental importance to the mission of the Office of Water,
and credible national estimates are of great utility to many EPA
programs. In particular, the estimates support the development of
risk assessments based on the ingestion of water that may be contaminated.
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Executive Summary
The objective of the report is to provide current estimates of
water ingestion for the population of the United States and selected
subpopulations. The subpopulations include gender and age categories,
pregnant women, lactating women and women of childbearing age. These
ingestion estimates may be used in estimating risk to human health
from the ingestion of contaminated waters. Knowledge of water ingestion
is of fundamental importance to the mission of the Office of Water,
and credible national estimates are of great utility to many EPA
programs. In particular, the estimates support the development of
risk assessments based on the ingestion of water that may be contaminated.
The Safe Drinking Water Act Amendments of 1996 require EPA to identify
subpopulations at elevated risk of health effects from exposure
to contaminants in drinking water and to conduct studies characterizing
health risk to sensitive populations from contaminants in drinking
water. The process of establishing human risk requires up–to–date
information on water ingestion and this report responds to that
need.
The reported estimates were calculated using data from the combined
1994, 1995, and 1996 Continuing Survey of Food Intakes by Individuals
(CSFII), conducted by the United States Department of Agriculture
(USDA). The CSFII is a complex, multistage area probability sample
of the entire United States and is conducted to survey the food
and beverage intake of the United States. The CSFII collected two
non–consecutive days of food ingestion data from a sample of
more than 15,000 individuals. The two days of dietary intake, in
conjunction with food code, recipe, and nutrient data from the USDA,
were used to identify the direct (plain drinking water) and indirect
water consumed by each respondent. Indirect water is defined as
water used in the final preparation of foods and beverages at home,
or by food service establishments such as school cafeterias and
restaurants. Quantities of ingested water reported were averaged
by participant to generate a two–day average. These daily average
ingestion amounts comprise the empirical distributions from which
mean and percentile per capita ingestion estimates are produced.
This report provides ingestion estimates of direct water, indirect
water and both direct and indirect water combined . Also provided
are water ingestion amounts by water source. Sources include community
water, bottled water, other sources, and all sources combined (total
water). Other sources include water from private household wells
and rain cisterns, and household and public springs.
Additionally, the report provides estimates of water consumption
for "all individuals" and for "consumers only".
The estimates for all individuals are based on all survey respondents
in the population (or subpopulation) under consideration including
those who reported no consumption of the water from the source under
consideration during the two survey days. The "consumers only"
estimates are based on only those respondents in the population
(or subpopulation) of interest who reported ingestion of the water
from the source under consideration during the two survey days and
excludes the "zero" consumers. All estimates are provided
in units of milliliters/person/day (ml/person/day) and milliliters/kilogram
of body weight/day (ml/kg/day).
The estimated mean two–day average per capita ingestion of
community water is 927 ml/person/day. This mean ingestion estimate
applies to all individuals in the United States population. A 90%
confidence interval about this mean ingestion ranges from 902 to
951 ml/person/day (See Table 4–1–B1). These estimates
of community water are based on a sample of 15,303 individuals in
the 50 United States and the District of Columbia. The sample was
selected to represent the entire population of the United States
based on 1990 census data.
The estimated 90th percentile of the empirical distribution of
two–day average per capita ingestion of community water is
2.016 liters/person/day. The 90% bootstrap interval about the 90th
percentile estimate ranges from 1.991 to 2.047 liters/person/day.
Therefore, current ingestion data indicate that 90 percent of the
United States population ingests an amount of community water which
is approximately less than or equal to the two liters/person/day
estimate used as a standard ingestion value by many federal agencies
(See Table 4–1–B1).
Women aged 15 to 44 years, the childbearing years, ingest a mean
of 922 ml of community water per day (90% confidence interval is
887 to 957 ml). This mean ingestion is similar to the mean daily
per capita ingestion of community water for the United States population.
Lactating women have the highest community water ingestion of any
subpopulation identified in the sample. Lactating women reported
a mean two–day average ingestion of 1.379 liters (90% confidence
interval is 1.021 to 1.737 ml/person/day). The 90th and 95th percentile
estimates of ingestion of community water for lactating women are
2.872 and 3.434 liters/day, respectively (See Table 4–1–E).
The estimates of community water ingestion based on "consumers
only" are higher than those based on all individuals because
respondents reporting zero community water ingestion during the
two survey days are excluded from the analysis. For "consumers
only," the estimated mean two–day average per capita ingestion
of community water is 1.0 liter/person/day (90% confidence interval
is 976 to 1,024 ml/person/day). These estimates are based on the
14,012 respondents to the CSFII who reported consuming community
water. The estimated 90th percentile of consumption is 2.069 liters/person/day
(See Table 4–2–B1).
The highest consumption estimates (and therefore most conservative
with regard to risk) are for total water ingestion by "consumers
only." The estimated mean ingestion of total water by "consumers
only" is 1,241 ml/person/day (90% confidence interval is 1,208
to 1,274 ml/person/day). The estimated 90th and 95th percentiles
are 2,345 ml/person/day and 2,922 ml/person/day, respectively (See
Table 4–2–A).
For babies younger than one year old the estimated mean community
water ingestion is 342 ml/person/day (90% confidence interval is
295 to 388 ml/person/day); the estimated 90th percentile is 878
ml/person/day (90% bootstrap interval is 849 to 918 ml/person/day);
and the 95th percentile is 1,040 ml/person/day (90% bootstrap interval
is 936 to 1121 ml/person/day) (See Table 4–1–B1). Thus,
the standard one liter ingestion rate used in risk assessments for
a 10–kilogram child is approximately less than or equal to
the 95th percentile of the empirical distribution of community water
ingestion for infants.
For babies younger than one year old who are water consumers, the
estimated mean total water ingestion is 563 ml/person/day (90% confidence
interval is 508 to 618 ml/person/day). The estimated 90th percentile
is 968 ml/person/day (90% bootstrap interval is 940 to 1,121 ml/person/day),
and the estimated 95th percentile is 1,236 ml/person/day (90% bootstrap
interval is 1,121 to 1,282 ml/person/day). Thus, the one liter standard
used in risk assessments for a 10–kilogram child is approximately
less than or equal to the 90th percentile of the empirical distribution
of total water ingestion for babies less than one year old when
considering "consumers only" (See Table 4–2–D1).
The Recommended Dietary Allowances (RDA, 1989) for water intake
are 1.5 ml/K cal and 980 K cal/day for a child between six months
and one year old. Thus, the RDA for a 10–kilogram child is
equivalent to 1,275 ml of water/day. Therefore, the default of 1
liter/10–kg child/day is slightly lower than the RDA value
of 1,275 milliliters per child per day.
For children one to ten years old, the estimated mean community
water ingestion is 400 ml/person/day (90% confidence interval is
380 to 420 ml/person/day); the 90th percentile is 905 ml/person/day
(90% bootstrap interval is 863 to 935 ml/person/day) and the 95th
percentile is 1,118 ml/person/day (90% bootstrap interval is 1,079
to 1,143 ml/person/day), respectively (See Table 4–1–B1).
Thus, the standard one liter ingestion rate used for risk assessments
for a 10–kilogram child lies between the 90th and 95th percentiles
of the empirical distribution of community water ingestion for children
one to ten years old.
For children one to ten years old who consume water, the estimated
mean total water ingestion is 532 ml/person/day (90% confidence
interval is 509 to 556 ml/person/day). The estimated 90th percentile
of total water ingestion is 1,004 ml/person/day (90% bootstrap interval
is 980 to 1,030 ml/person/day), and the estimated 95th percentile
is 1,242 ml/person/day (90% bootstrap interval is 1,198 to 1,284
ml/person/day) (See Table 4–2–D1). Thus, the one liter
standard ingestion used in risk assessments for a 10–kilogram
child is approximately less than or equal to the 90th percentile
of the empirical distributions of total water ingestion for children
one to ten years old when considering "consumers only."
When considering water ingestion rates based on units of milliliters
per kilogram of body weight per day, this analysis shows that the
mean ingestion rates for babies younger than one year are estimated
to be three to four times higher than the mean rates for the population
as a whole. For example, the estimated community water ingestion
rate is 46 ml/kg/day (90% confidence interval is 39 to 53 ml/kg/day)
for babies in the U.S. population versus 16 ml/kg/day (90% confidence
interval is 15 to 16 ml/kg/day) for the general population (See
Table 4–1–B2). The estimated community water ingestion
rate for babies consuming community water is 69 ml/kg/day (90% confidence
interval is 62 to 77 ml/kg/day) versus 17 ml/kg/day (90% confidence
interval is 16 to 17 ml/person/day) for the general population (See
Table 4–2–B2).
The mean per capita ingestion of community water is 75 percent
of the mean total water ingested from all sources. The mean bottled
water ingested is 13 percent of the mean of total water ingestion,
while water from other sources such as wells and rain cisterns is
10 percent of the mean of total water ingested.
Many federal agencies, including EPA, use the standard water ingestion
quantities of two liters for a 70–kilogram adult and one liter
for a 10–kilogram child. This 2–liter quantity of ingested
water is supported by a National Cancer Institute (NCI) analysis
of the USDA 1977–78 USDA National Food Consumption Survey (NFCS)
data (1989, Ershow and Cantor). The mean per capita daily intake
of tap water, as estimated from the 1977–78 NFCS data is 1.193
liters/person/day. The estimated percentile corresponding to two
liters per day ingested is the 88th. There are a number of differences
in the methodologies used in the Ershow and Cantor study and this
analysis. One difference is that the Ershow and Cantor estimates
were based on 1977–78 data while the estimates in this document
are based on data collected in 1994 through 1996. A second difference
is that the 1977–78 NFCS was based on three consecutive days
of food intake while the 1994–96 CSFII was based on two non–consecutive
days. A third difference is that the Ershow and Cantor report defined
tap water as "water from the household tap." In this report,
water coming from the tap is distinguished by source. Sources of
water coming from the tap may include: community water, household
well or cistern, a household or public spring, and other. Another
way that the estimates in this report differ from those in the 1989
report is that the 1994–96 data include water ingestion by
pregnant and lactating women. These women were excluded from the
1989 report.
The CSFII surveys have advantages and limitations for estimating
per capita water ingestion. The primary advantage of the CSFII surveys
is that they were designed and conducted by the USDA to support
unbiased estimation of food consumption across the population in
the United States and the District of Columbia. One limitation of
the CSFII surveys is that individual food consumption data were
collected for only two days—a brief period which does not necessarily
depict "usual intake." Usual dietary intake is defined
as "the long–run average of daily intakes by an individual."
Upper percentile estimates may differ for short–term and long–term
data because short term food consumption data tend to be inherently
more variable. It is important to note, however, that variability
due to duration of the survey does not result in bias of estimates
of overall mean consumption levels. A second limitation is that
the multistage survey design does not support interval estimates
for many of the subpopulations reported in this document because
of sparse representation in the sample. Therefore, only mean and
percentile estimates are reported for all subpopulations considered
here. The survey does support interval estimates for the U.S. population
and some large subpopulations which are presented in Chapter 4.
A third limitation is that the survey design does not support generating
water consumption estimates for certain subpopulations of interest.
Examples of such subpopulations are Native Americans with traditional
lifestyles, people who live in hot climates, people who consume
large amounts of water because of physical activity, and people
with medical conditions necessitating increased water intake. While
these individuals are participants in the survey, they are not present
in sufficient numbers to support water ingestion estimates.
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