Your sperms watery doesn't mean you shot blank... unless you have a report from your doctor said you don't have any sperms in you...then you might have a doubt of your wife.. if not.. it is possible for your wife conceive once you ejecuate into her...
Are you saying you have been tested and they said you have watery sperm cells? Or are you saying your *** your fluid you ejactulate is like water? If you are saying your fluid is like water that has nothing to do with the sperm just what they live in. You could of got her pregnant. Once you went in her then her cervical fluid takes over and it has the same properties as semenal fluid. It has protein and all to keep the sperm alive till they find the egg. Are you not happy she is pregnant or just worried it is not yours?
If you had intercourse there is always a possibility...
You need to talk to medical provider for this issue...