BPC is very unstable, always keep the vial in the fridge and avoid shaking, in powder form should last about 1 year.
To reconstitute sterilize both rubbers caps (BPC vial and bacteriostatic vial), inject with the syringe onto the vial wall, not on the powder, do it gently, don't shake, just roll the vial between the fingers, it dissolves easy and fast, eventually place in the fridge and wait a few minutes.
Use a new and sterile syringe, don't touch the needle, bacteria are the enemy, if they enter the BPC vial will start multiply and spoil everything.
Once reconstituted always keep in the fridge, it will last a couple of weeks, maybe 3 but better to play safe, if it turns cloudy is gone bad.
No need for adding it to drinking water for oral route in my opinion, just squirt it under your tongue and keep it there for 10-15 minutes in order to get it sublingual.
It isn't 100% clear if oral is fully effective, for "digestive" (stomach-intestine) seems established, for other parts of the body should but we don't know exactly if one needs more or what, in mice studies it seems that oral or injected provided same effectiveness,
To play safe subq injection is guarantee to go fully systemic and since the amount is really tiny isn't big deal, that's the most commonly used route.
If you really dislike pinning sublingual would be a good choice, I guess.
Always use new and sterile syringes, never enter the vials with used syringes, it doesn't matter if you are going to pin or not, bacteria will spoil BPC!