I bought 10,000iu of HCG, however it came as a 10,000/1ml solution. I want to add 3 more ml to it but I have no clue what type of water is in there. I will be using bac water to recon the other bottle I have. Is it fine to add the same bac water to the 10k bottle? I have heard DO NOT mix waters but no actual reasons why.
I think you will be alright if you mix different bw. But if are worried order some more water and use it when it gets in. Otherwise use the water you have and do the math for proper dosing.
It's usually just sterile water that is provided with most HCG. It's really only designed to for single use. I would recommend using BAC water.