Can drinking a lot of water make vaginal discharge more watery?

No: That doesn't happen. The water in cervical mucus is regulated by the circulating estradiol levels, that is not affected by how much water you drink.

Not likely: drinking lots of water is healthy. if you are older and have incontinence issues, drinking a lot of water can overfill your bladder and make you leak a bit. diabetes can do this as well because your bladder can overfill without you being aware.