UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WSG 66A
Date Signed: August 21, 1991
MEMORANDUM
SUBJECT: Definitions of Types of Public Water Systems and
Populations Served by Those Systems
FROM: Connie Bosnia, Chief (Signed by Ray Enyeart) . '•
Drinking Water Branch
TO: Drinking Water/Groundwater Protection Branch Chiefs
Regions I-X
We have been asked several times recently to define what constitutes the "population
served" of transient and nontransient noncommunity water systems (TNCWS & NTNCWS). In
the process of drafting guidance on populations we realized that we needed to refer to other terms
which also beg for clarification. We, therefore, believe this is a good opportunity to reiterate
definitions related to the types of water systems, and in some cases, to define terms for the first
time. We have also included a flow chart that rriay.be helpful in deciding what type of system a
water supply is. While we have attempted, through these definitions and flowchart, to be as
specific as possible, we realize that this guidance is not, and probably could not be, a cookbook.
We do believe, however, that the document offers sufficient definitions and explanations to allow
for reasonable and consistent decisions on system categorization and population identification.
SYSTEM TYPE: , ;f-: ^'.-.^
.' :..-'••• .'.• - . '.-' ' - - . • '
Probably the best place to begin is with the National Primary Drinking Water Regulation
(NPDWR) definitions of the various types of water systems. Excerpts of those definitions follow.
Emphasis has been added to highlight the pivotal criteria.
PWS "has at least fifteen service connections or regularly serves an average of at
least twenty-five individuals daily, at least 60 days out of the year."
CWS "a public water system which serves at least 15 service connections used by
year-round residents or regularly serves at least 25 year-round residents. "
..NCWS "a public water system that is not a community water system. "
NTNCWS "a public water system that is not a community water system and regularly
serves at least 25 of the same persons over 6 months per year.
TNCWS Not defined in regulation. Implied to be any NCWS which is not a
NTNCWS.
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WSG 66A
The above definitions contain two terms which in turn require some explanation - "year-round
residents" and "same persons." We would define these terms as follows:
Year-Round Resident (or Residential Consumer)
an individual whose primary residence is served by the water system. [The
individual need not live at the residence for 365 days a year for it to be considered
his/her year-round residence.]
Same Persons (i.e., Non-Residential but a Regular Consumer)
an individual who does not reside at a place-served by the water system, but has 'a
regular opportunity to consume water produced by the system, fObvious examples
are children at school and employees at their workplace.] ;
We provided guidance earlier (September 16,1987) on how much time a person had to have
access to a water system to be considered a regular consuriier. Ift sujnniary, that guidance said:
Regular opportunity (or regular access)
//.•:/;.'".v:-'r "*•. '' :••':•'
four or more hours per day,/or four or more days per week, for 26 or more weeks
per year. ,•;••''•' •'•' ;v-':':;/•'.'•• •
There is another term which should be defined because it is used frequently, even though it
does not appear in the NPDWRs - "transient or transient consumer." We offer the following
definition: V; A;' - „
•••••.. .• :-.-••••' •-.- • • ••'•';•''.
Transient Consumer
^individual who has the opportunity, to consume water from a water system, but
whfy does not fit the definition of a residential or regular consumer. [Obvious
examples are people stopping by at a highway rest stop, people vacationing for a
few days prweeks,at a hotel or resort, people having lunch or dinner at a
restaurant,'etc.]
SYSTEM POPULATION:
With the types of systems defined, we can define the populations served by each.
Population Served (for any type of system)
The number of residential consumers plus the average of the number of regular
consumers served, per day, during a month plus the average of the number of
transient consumers served, per day, during a month.
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WSG 66A
The averages of the regular and transient consumers may (and most likely will) change
from month to month, and season to season. For the purposes of determining compliance with the
State (or Federal) regulations, we propose that the State have the option to decide whether to keep
the population served as a fixed number throughout the entire year, or to change it from season to
season. If, however, the choice is to keep a fixed number (which is what we recommend), it
should be the highest average daily population that would occur during the year. For purposes of
reporting to the Federal Reporting Data System (FRDS), the population served [data element
Cl 17] could also change each quarter since States have the ability to change inventory information
in FRDS on a quarterly basis. Again, we would prefer that the reported populations remain as
stable as possible, and therefore suggest that the population reported to FRDS be the highest
average daily population that would occur during the year.
Following are a few examples of determining the-type of water system and its population:
Example 1: A system, solely serving a small restauran|3 has no residential consumers, 10
employees (regular consumers), and serves: an average of 300 customers
(transient consumers) per day, year round. The system is a transient
noncommunity water system, serving a population of 310 (O residents +10
regular consumers + an average of 3pO transients /day).
Example 2: A system, solely serving a campground/lake/swimming beach of a State
park, serves 4 people in the park ranger's residence (residential consumers),
20 cabins (estimated by the State - 300 people), and averages another 250
visitors per day that swirn at the lake's beach. During the fall and spring the
20 cabins afe only partially occupied, and usually just on the weekends, the
campground is closed but the lake is still open for boating. During the
winter only the park ranger's residence is in operation. The system is a
transient,noncommunity water system since it does not have 25 or more
residential consumers and it does not have 25 or more regular consumers for
more than 6 months per year. The system has an average population of 604
(4 residents + 50 regular consumers + 300 transient consumers + 250
transient consumers) during the most populous month.
Example 3: A system, solely serving a rural elementary school, serves the principal and
6 teachers and 85 students. The school is in operation for 9 months of the
year. The system is a nontransient noncommunity water system because it
serves 25 or more regular consumers for more than 6 months per year. The
system has an average population of 92 (7 regular consumers + 85 regular
consumers).
Example 4: A system, serves a church, the minister's home, and 2 neighboring homes.
There are 5 people that reside in the minister's home, and a total of 7 people
that reside in the neighboring homes. The church operates a year-round
preschool which has 2 teachers and 15 children. The system is a
nontransient noncommunity water system because it serves a total of 12
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WSG 66A
residential consumers and 17 regular consumers, which are served for 6 or more
months. An average of 100 parishioners attend church or Sunday school each
Sunday. In addition, the church holds other functions such as choir practices, youth
group meetings, and dinners. The daily average, over any given month, for the
transient population is 25 people. The system has an average population of 54 (12
residents +17 regular consumers + 25 transient consumers).
We request your review and comment on the above. Unless there are major disagreements
with the proposal, we plan to issue the definitions as a Water Supply Guidance. If, however, there
appear to be significant or sufficient objections to the proposal, we will re-group and re-propose a
definition, or set up some type of forum to resolve the objections. Please call, or send, any
comments to Ray Enyeart on 382-5551. I would appreciate your feedback by September 30.
Thanks.
Attachment:
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WSG 66A
Flowchart for Determination of PWS, CWS, NTNCWS and TNCWS
Does the supply have 15 or more service
connections, or serve 25 or more consumers/day
for 60 or more days/yr?
Are 25 or more consumers/day
ever the same consumers?
Are the 25 or more same
consumers/day served 60 or more days/yr?
Are the 25 or more same consumers
served more than 6 months/yr?
Not a PWS
Are the 25 or more same consumers/day
year-round residents?
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