Marlene Moore
Advanced Systems, Inc.
mmoore@advancedsys.com
OBJECTIVE
Present perspectives on Metrological Traceability of
Water
Provide background on regulatory science versus
theoretical science
Testing and Calibration aspects related to Water
TRACEABILITY OF WATER
Not possible unless you are talking about water sources
Where does my water come from?
Sources: River, groundwater, ocean, surface water,
etc…..
These are not SI but we can trace the water….
TRACEABILITY OF WATER
When measuring water our first question is:
What will the water be used for?
Knowing the answer will define the measurement requirements:
Drinking water : 40 CFR Part 141
Wastewater: 40 CFR Part 136
Reagent Water used in testing: ASTM D1193
Purified Water : USP <645>
Bottled Water, Cleaning Water, etc….
TRACEABILITY OF WATER
Water - Used everywhere – but little understood
When measuring water:
Specification related to the use of the water in a process or
activity. (drinking water, treatment, manufacturing, processes,
etc.)
Looking for impurities that affect the water
Measuring a characteristic of the water that is an industry
standard for defining the quality – often quick and easy
measurement…
TRACEABILITY OF WATER
Therefore…
We are looking at a measurand:
-- define a concentration or amount of a contaminant or
substance in the water
-- the amount is NOT traceable to the SI in the pure sense,
but is traceable to a reference material that has been
defined as suitable for that use
REGULATORY SCIENCE
FDA, EPA, Nuclear Commission, state, local and industry have
specifications for water
These specifications require measurements to determine if the
water can be used for a specific application (e.g. drinking,
pharmaceutical, nuclear, etc.)
The specification requires a measurement using a specific reference
material, method and controls
MOST OFTEN NOT WRITTEN IN METROLOGICAL TERMS!
Results in confusion and misunderstandings
TESTING NOT CALIBRATION OF WATER
Therefore we are testing water not calibrating water.
When we perform testing of water we are looking for traceability to
the SI of the measurement or measurand.
Conductivity in treated, process or drinking water
pH – Harned Cell – IUPAC convention –
Primary method traceability not SI
Total Organic Carbon (TOC) – Reference material
Potassium hydrogen phthalate, (KHP)
NO NIST SRM for TOC
TESTING
Calibration is part of the testing performed. Calibration is performed
just prior to the testing and includes Quality Control to verify no
significant drift or problems occurred during testing
Equipment Servicing confused with calibration
Most regulatory programs may require calibration 1/year
Default from older units where failure more common
Calibration of the meter without the probe has been observed and
therefore the calibration is not performed to the measurand
(conductivity, pH)
Calibration TOC is defined by the test method traceability is to the
method and RM.
Instrument calibration to mfg specs - a problem
SUMMARY
Testing labs and calibration labs must understand the reason
for the measurement.
When measuring water to specifications you are most often
testing with calibration being part of the process.
The calibration is often an insignificant or minor contributor
to the overall process. (After all other influence quantities
have been controlled)