Sterility assurance is a process, not a claim
Pharmaceutical grade bacteriostatic water is manufactured under recognised GMP frameworks with batch records, validated sterilisation and documented sterility assurance. The label is the tail end of a documented process.
Generic imports frequently arrive with none of that paperwork. The sterility claim sits on a printed label with no batch documentation behind it. When we say batch documentation is available on request, that is a documented chain, not a marketing line.
pH is the quiet variable
Preserved water should sit near neutral pH, typically 4.5 to 7.0 for a preserved injection-grade product, and critically, consistent batch to batch. Some imported stock drifts alkaline, and a drift outside the expected range changes reconstitution behaviour.
Researchers chasing a strange result often blame the compound when the diluent is the variable. Consistent pH matters as much as sterility, and it is one of the first things cheap manufacture gives up.
Benzyl alcohol content: 0.9% means 0.9%
The preservative load in pharmaceutical grade product is specified and verified at 0.9%. Import product has been found under-preserved, which shortens effective vial life, or over-preserved, which changes the solution profile.
Either way you are running your protocol on an unverified input. A $2 saving per vial is a poor trade for an uncontrolled variable in every vial that follows.
What this means at the bench
Use pharmaceutical grade, batch documented product. If a result looks off, the diluent should not be on your list of suspects. BuyBac ships pharmaceutical grade bacteriostatic water in 10mL, 30mL and 5x10mL formats, batch documented on request, dispatched from Perth.