ACTUALLY......
Just because two substances are water based doesnt necessarily mean they're okay to mix together. I know one of the possible consequences of doing this first hand.
One time when my wife was taking injectable bovine placenta extract I accidentally opened an amp and injected it into a vial of HGH thinking it was the sterile water. Later, after injecting half the vial, I realized my mistake but thought "fuck it, ill be fine" and injected the other half later that day.
After about a day or two I noticed the injection sites under my navel were hard lumps-but not red, swollen, or anything. Just hard lumps. Apparently my body had not recognized the mixture as safe and walled it off into two sterile abcesses. These sterile pockets sat under my skin as hard lumps for weeks until one day the first one finally came to suface and leaked out pus. About 12 hours later the second one followed suit. But the worst thing about it was they made two horrible, purplish scars where they had been pushed out of my body.
Now I still have two Purple scars resembling cigarette burns below and to each side of my belly button although they have shrunk and lightened up considerably. Moral of the story, dont go mixing active substances to inject unless you know beforehand its okay. That said, I am nearly positive hcg and hgh will be fine.