I have to share this with you.  Every single time I make egg salad for sandwiches the next day the leftovers are always watery.  I made some the other day (Wednesday) and it is not watery.  My trick.....I chopped the onions and salted them and let them "breathe" for about 15 minutes.  Knocked off any excess water.  Then added them to the salad mixture.  I just made a sandwich and no water.  I did this with cukes too!