Every time my penis gets hard, I have to keep running a lot of transparent water. What's the disease?

This is not a disease, it is a normal physiological phenomenon. When a man is excited, his penis will erect and automatically secrete a transparent liquid called prostatic fluid.

In addition, it also contains a small amount of sperm, so when making love, both men and women may get pregnant even if they don't ejaculate in the vagina, because there will be a small amount of sperm flowing out of the early liquid, but the probability of pregnancy is relatively small.