Low Sperm Count (Oligospermia): A sudden change in semen consistency, such as watery semen, could be due to a low sperm count. This condition can be caused by various factors, including hormonal imbalances, testicular issues, or blockages in the reproductive tract.

Retrograde Ejaculation: This condition occurs when semen enters the bladder instead of exiting through the penis during ejaculation, resulting in a reduced or watery semen volume.
Prostate Issues: An inflamed or infected prostate gland (prostatitis) can cause changes in semen consistency, including watery semen.
Semen Leakage: Leakage of semen from the urethra or other parts of the reproductive tract can lead to a watery or reduced semen volume.
Hormonal Imbalance: Hormonal changes, particularly low testosterone levels, can affect semen quality and consistency.

Testicular Cancer: Although rare, testicular cancer can cause changes in semen consistency, including watery semen. It is essential to rule out this potentially life-threatening condition.
Epididymitis: Inflammation of the epididymis, a tube at the back of the testicle that stores and carries sperm, can cause changes in semen consistency and may lead to more severe complications if left untreated.

Young's Syndrome: A rare condition characterized by obstructive azoospermia (blockage of sperm flow) and chronic sinopulmonary infections, which can cause changes in semen consistency.
Cystic Fibrosis: A genetic disorder that can cause congenital absence of the vas deferens, leading to low or absent sperm count and potentially watery semen.
Medication Side Effects: Certain medications, such as alpha-blockers or antidepressants, can affect semen quality and consistency, although this is a rare cause of watery semen.