GnRH stimulates (causes) the pituitary gland to produce follicle stimulating hormone (FSH), the hormone responsible for starting follicle (egg) development and causing the level of estrogen (the primary female hormone) to rise
So basically estrogen for females and testosterone for males.
because to irrigate you need purified or rain water to not kill your plants/animals and once you've used your fresh water how would you get more purified water?