Remember that everything depends on the I.U. rating of your HCG. Some of them are 2500iu/ml some 5000 and I think some are even 10000. If you add extra water you lower your I.U./ml proportionally but it can be easier that way than trying to deal with 1/10th ml, especially if you're using a regular syringe. Slin pins are ideal because they only hold one ml and it's broken down into 100ths by 10s.

You gotta be careful not to overdose on this because from what I've read you can permanently desensitize your nads to your natural LH/FSH (or whatever it is HCG mimics) if you use too much HCG too long.