how much sodium?

you much sodium do you need (% wise, or mg wise) to retain water?

I think it's different for people.
A few days ago I binged and had an extra 160% of my RDA of sodium and gained about 5-6 pounds. =/

It's a combination of too much salt (also sugar, caffeine and alcohol) and not enough fluids.... If you eat salty foods but drink plenty of water you could mitigate the effects.  However, for good health it's best not to overdo the salt on too regular a basis.

You need about 500-1000mg sodium per day but don't go over 2400mg of sodium