Can a woman become pregnant if you don't use a condom, only from "before-sperm liquid"? It's not sperm. This liquid comes when a man is aroused.
This "pre-ejaculate" that you are talking about does contain a very small amount of sperm, and can absolutely cause pregnancy. To be clear, the alkaline fluid that comes out as the pre-ejaculate is made in Cowper's glands, which do not produce sperm. However, sperm may be present from a prior ejaculation and come out as part of the pre-ejaculate.
The article above goes into some detail. Basically, there is a 41% chance of the content having sperm, and a 37% chance that the sperm it contains are motile - enough to swim upstream and potentially fertilize an egg.
Actual fertilization depends on a lot of things. However, if you do this enough, the odds of pregnancy increase.