Water Boards adds a "blank water modified" matrix for specific toxicity controls; staff flag inconsistent use of "lab water"

Staff announced a new matrix specifically to support a toxicity testing control used when an alternate control is required to test whether conductivity or salinity in a sample affects test organisms. Tessa said the sample-type code for that control is CNSL and that the new matrix — described as "blank water modified" — is "specifically for use with the CNSL test type sample sample types." She emphasized the matrix should be used only for that limited purpose and not as a general blank. Attendees raised related issues: toxicity and chemistry templates differ in how they record controls, some labs historically used a separate lab-water code rather than blank water, and chemistry control types such as laboratory control spike (LCS) or matrix spikes have parallels to modified blanks. Tori and other lab-affiliated participants said their contracted labs have long used the lab-water code and asked staff to verify whether the lab-water description reflects how labs actually prepare that water (for instance, laboratories sometimes mix reagent-grade or modified hard water tailored to the organism). On the lab-water matrix, Tessa noted the current description says "unprocessed laboratory tap water," and she questioned whether that matched laboratory practice. Participants suggested either clarifying the lab-water description or keeping the code but updating the description to align with how labs prepare organism-supporting waters. Why this matters: accurate matrix and sample-type coding matters for data interpretation and quality-control analyses; inconsistent use of lab-water versus blank-water codes could confuse comparisons and lead to misinterpretation of control or QC results.