from a masturbation Q&A site regarding your question:
Don't get me wrong, I know that on the Internet people sell all kinds of enhancement and enlargement pills that don't work. I know that you can't make your penis bigger with pills. But what about ejaculate size? Can vitamin supplements or special "volume" pills make you ejaculate as much as 500% more? Peter North, a man known for big ejaculations, is the poster boy for one kind of enhancement pill. Is there any truth to their claims?
Well, you're correct that a pill is more likely to make you ejaculate more than it is to make your penis grow (which is impossible). However, whatever a pill company's claims are, you can probably do just as well with zinc and lecithin supplements. (Use zinc supplements in moderation; too much zinc intake can be dangerous.) For some guys, these nutrients do have a noticeable effect on ejaculation volume, and they're a lot cheaper and easier to get. In general, stay away from mail-order pills sold by less-than-reputable companies; you really don't know what's in them, and their claims are almost always untrue or at least greatly exaggerated. Finally, on the social responsibility side, you should never do anything to support businesses that advertise via spam or that target people's sexual insecurities.
Why is it that drinking water hours before you masturbate increases the volume of semen?
Good question. I think it's because your body becomes more hydrated overall, so any glands responsible for secreting a watery substance (such as those in the male reproductive system) are able to work more efficiently and have less trouble getting water from the bloodstream. If you're dehydrated, on the other hand, your body will want to conserve water, so these glands will not have as much water available, and you'll ejaculate less.