You reconstitute it with Bacteriostatic Water which is available without a prescription in the USA and contains 0.9% benzyl alcohol to inhibit bacterial growth.
If you're particularly concerned you buy a 0.22 micrometer PVDF "syringe filter" and pump it through that to another, fresh/sealed sterile vial which you can get for like $2.00 from a medical supply company (the syringe, filter, and vials are gamma-irradiated to destroy any remnants of RNA/DNA). That size filtration will filter out any lifeforms (fungal, bacterial, viral) while allowing the peptide/drug itself to pass through. So you get a guaranteed sterile solution out of the filter.
0.22 won't filter out viruses, but time will inactivate enveloped viruses (which are usually the ones you want to avoid injecting), and source control/proper handling should take care of the rest.
The same distributor sells legal things to import like L-Carnitine, Epitalon, Berberine, NAD+, NACET, and vitamins at great prices so I was saying I use them for things like that.
But others use them for GLP-1 agonists and many do their own independent testing.