DO you mean that you have to run and pee? or that you are puffed out with that O So flattering water retention thing??
Either way it probably isn't the salad. I know that salad is mostly water but by volume it can't be as much as a couple of glasses of straight water, which would not have that effect. Unless your salad is very salty with some dressing or other, or you are in the early days of drinking more water in which case I think it can have the 'running to pee' effect more. After a while that seems to settle down to some extent, particularly at night. I no longer get up for a pee. Which is good.
I think water retention is very odd and not predictable.
Not a very helpful reply, as I am basically saying I do not know, but with all these things, it will probably get better as your body settles down to what might be a big change in chemistry.