Semen is the liquid substance that leaves the body during ejaculation, sperm are the mobile cells within the semen that cause fertilization. On average, only 5% (by volume) of semen consists of sperm cells, and of that, fully 25-50% of the sperm are dead or abnormal and incapable of producing offspring. To understand what causes watery semen, it is necessary to understand what the more solid parts of semen are and why they are not causing the proper thickness to the semen.
There are four major parts of the male reproductive system that contribute to the formation of semen. The testicles are responsible for providing the sperm who´s purpose it is to fertilize the female. The seminal vessicle produces a substance that is rich in the sugar fructose. This fluid constitutes over 50% of total volume of semen and the fructose is used as fuel for the sperm. The prostate gland contributes about 25% of semen volume and it´s purpose is to neutralize the acidic environment of the female´s vagina. If this part of semen is missing, the sperm will be killed by the acidity of the vagina. The final contributer is the bulbourethral glands, which contribute a lubricant that preceeds ejaculation and increases the speed at which the ejaculant leaves the body. This allows the semen to be deposited deeper within the female and increases chances for fertilization.
There are a few causes for clear, thin and watery semen, and a few simple solutions.
1. Insufficient sperm count - The most common cause of this is frequent ejaculation. In very sexually active individuals, or individuals who masterbate often, the testicals simply do not have enough time to produce produce sperm cells. The average sperm cell takes 70 days to mature and be ready for ejaculation. While each ejaculation does not empty the testicals of sperm cells, after a few days of frequent ejaculation, the testes will become depleted and no longer contribute sperm to the semen. The only way to restore them is to avoid ejaculation for awhile. There is also a chance that a zinc deficiency is leading to a low sperm count so if watery sperm is a concern, make sure you are getting the proper nutrients in your diet.
2. Fructose deficiency - Fructose comes mainly from fruits and vegetables. There are a few conditions that would leave the body deprived of fructose and cause the semen to appear watery. Most notable would be a diet that lacks the necessary carbohydrates and sugars. Either because of poverty or vanity, a diet with insufficient energy will produce semen that is lacking in fructose. Secondly, overexercising can often lead to this condition as the body uses sugar to provide energy for the exercise. In most cases, the solution is to simply make sure to eat more fruit and vegatables.
It is important to note that both conditions can lower fertility rates, so if you are trying to conceive, semen quality is important.