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Utility managers in the United States might want to steal a trick
from the bags of their English colleagues. In the UK, measurement of
heterotrophic plate count (HPC) is required for all regulatory
drinking-water samples. This ensures that operators are using this
valuable tool to monitor the condition of their drinking-water
systems.
The theory is to measure HPC in drinking-water pipes for the
purpose of monitoring trends in counts. Samples from a given location
will typically fall within a certain range of HPC/mL, depending on the
type of source water and season of the year. Departures from that
range are often a warning that coliform contamination is around the
corner.
| A dramatic spike in heterotrophic plate count typically signals
a new source of contamination, for example, a crack in a main or
storage reservoir that is allowing dirt or other contamination into
the system. If an HPC test produces such a result, best practices
suggest investigative sampling, including coliform sampling, in the
area to characterize the specific location and nature of the
problem. |
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Plate count agar and
SimPlate for HPC are the only EPA-approved methods for HPC
analysis in the U.S.
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A gradual rise in HPC over time can be indicative of biofilm
growth. As biofilms accumulate along pipe walls, they provide a haven
for bacterial growth—the more biofilm, the higher the potential HPC
count. As the biofilm increases, patches of interwoven bacterial
colonies can "tear off," sometimes releasing coliforms that are
capable of growing within the biofilm. Monitoring HPC trends can give
operators a clear picture of when best to clean pipes through chlorine
shocking or high-pressure flushing.
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TECH TIP
SimPlate for HPC can be run with 1 mL of
sample or 10 mL of sample for increased sensitivity.
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At Manchester Water Works in Manchester, New Hampshire, HPC
testing plays an important role in measuring water quality. "We use
HPC results to measure disinfection residual, but we also track
results over time at certain sample sites," says laboratory manager
Cheryl Wood. Tracking HPC results alongside other parameters, like
disinfection residual and turbidity, helps Manchester better manage
the quality of the water in the distribution system. "HPC data helps
us make adjustments to disinfection residual and plays an important
part in determining when and where lines might need to be flushed.
HPC testing helps us do the best job that we can," says Wood.
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Wood's lab uses the IDEXX SimPlate for HPC test. "An advantage to SimPlate is
that there is no need for media preparation. During peak testing
times, SimPlate helps us because it is easy to use," adds Wood.
The SimPlate for HPC test is an easy, rapid and accurate test for
HPC. Approved by the U.S. EPA, SimPlate for HPC results correlate to
those obtained with plate count agar. SimPlate for HPC is easy to read
and less subjective than plate count agar. In addition, quality
control (QC) is simplified with SimPlate for HPC as QC checks are
only needed on a per lot basis, and not for daily media batches.
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