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Council clarifies 'blank water' and lab-water uses; proposes 'tap water' matrix for field QC
Summary
Staff told users blank water should represent reagent or appropriate-purity QC water, lab water (currently defined as unprocessed tap water) has been misused, and the team will add a distinct 'tap water' matrix for limited field-QC uses where tap water has been tested and shown free of target analytes.
During the December meeting, Tessa Foggitt said the Council will clarify definitions for blank water and lab water to reduce inconsistent use in the database and will add a 'tap water' matrix option for specific field-quality-control uses.
"Blank water...should be any type of reagent water," Foggitt said, explaining blank water is intended for QC samples and controls (including toxicity controls) and should reflect the appropriate purity for the test. She noted that lab water is currently described as "unprocessed laboratory tap water," language that has led some users to select the matrix incorrectly for controls.
Foggitt described circumstances where using tap water for field QC can be acceptable: if the tap water has been tested for the same target analytes and shown to be free of them. "So we would just add a name of tap water to be really clear to people like this," she said, signaling the team will add a distinct tap-water matrix rather than leaving 'lab water' ambiguous.
Staff said they will coordinate with data providers and regional data centers on the change; users may request retrospective updates to past records through their RDCs, but database managers will not perform a system-wide retroactive edit without provider requests.
The proposed changes are intended to reduce confusion and improve consistent recording of QC and control samples across chemistry and toxicity datasets.
