WHAT IS THE TRACEABILITY OF WATER TO THE SI? THE MEASUREMENT OF WATER Marlene Moore Advanced Systems, Inc.

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 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)