Has anyone dealt with bacteriostatic water sourcing and sterility considerations?

Answering the narrow version, because the broad one does not have a single answer. Do it in two steps and it stops being confusing. First concentration: 10mg into 2ml is 5mg/ml. Then volume: a 0.5mg dose is 0.5 ÷ 5 = 0.1ml. Then units, and this is where people go wrong — a U-100 syringe is graduated in hundredths of a millilitre, so 0.1ml is 10 units. The word "units" has nothing to do with milligrams; it is a volume marking that exists because insulin happens to come at 100 units per ml.

Dr.RaviCardio said:

Do it in two steps and it stops being confusing.

Agreeing with Dr.RaviCardio, and the qualification matters more than the agreement. The arithmetic is right and one caveat matters: a U-40 syringe changes the markings, not the volumes. If someone hands you U-40 and you read it as U-100 you will be 2.5 times out, and that error has a direction — it is always an overdose.

I would rather be corrected than agreed with, if it comes to it.

traveltech_sara said:

I reconstituted a 10mg vial with 2ml of bacteriostatic water and I want someone to check my unit arithmetic before I draw anything, because I keep…

Can confirm the pattern traveltech_sara describes. Concentration choice is a precision decision, not a preference. Reconstitute high and every dose is a tiny volume where one unit of syringe error is a large fraction of the dose. Reconstitute low and you get more graduations per dose, so the same hand tremor costs proportionally less. Against that, more diluent means more benzyl alcohol and a shorter comfortable in-use window.

Ask again with the specifics and you will get a better answer than this one.

From the other side of the consultation, briefly.

Ongoing cost tracking for dosing arithmetic — transparency for the community:

Monthly medication cost: $144
Supplies (syringes, BAC water, alcohol swabs): ~$12/month
Janoshik testing: ~$14/month (amortized quarterly)
Lab work: ~$44/month (amortized quarterly)
Total: ~$174/month

Compare to brand Wegovy at $1284/month without insurance. Compounded is roughly 90% cheaper for what I have found to be clinically equivalent medication.