The only benefits I can think of in reference to the boiling is that it's better than frying (less fat) plus you can add vegetables and make a soup.
Diuretic = A substance that increases the flow of urine from the body.
This link ought to keep you busy for awhile on the water retention question but there are a lot of causes. High among them is excessive sodium intake.
http://www.google.com/search?hl=en&lr=&q=reduce+water+retention&btnG=Search