Simple.
Water has a different density to oil.
When you simultaneously inject both water and oil-based ASS together you create an emulsion within the depot, which screws up the release rate of the two different AAS.
The wole point of water-based AAS is that they are released extremely fast intyo the blood stream from their injection site. Oil takes far longer(Hence why AAS w/ esters are all oil-based).
Also, having a water-based AAS inside an injection site for an extended period of time is a recipy for an abscess. Bacterial growth can occurr.
Fonz