Hi there I'm a 30y female and I get too wet during sex how can I control it and what is the cause.

The causes are several. One is the vagina secreting mucous and other fluids as part of normal function, often at mid month ovulation or during intercourse. The other is perspiration around the vulva, which have more sweat glands than any other part of the body, and some women just sweat more there than others. There isn't anything you can do about it that I know of, except stopping to towel yourself periodically. If your partner is complaining that you are so wet that there isn't enough friction, try putting 3 tampons in your vagina for a few minutes, and do Kegel exercises to keep your muscles strong, and practice squeezing your vaginal muscles.
Too bad there isn't a little towel he can wear... maybe get some plain cotton garden gloves for him to dry you out with.

Try kegels.
Kegel exercises: A how-to guide for women - MayoClinic.com (http://www.mayoclinic.com/health/kegel-exercises/WO00119)