Need help understanding water retention

That's known as pitting edema. Things to be investigated; congestive heart failure, liver dysfunction, kidney dysfunction & pulmonary hypertension. Your profile mentions prior surgeries which may have affected your lymphatic system depending on what surgeries you had. Its also possible to get such edema from prolonged sitting. Another thing to check is your blood sodium level. Some people have similar edema with no apparent cause and otherwise good health.
You might try cutting sodium intake to 1500 to 1600 mg daily and see if that helps.

Oh you hit a spot with me. I'm a nerd.

Pretty much, sodium is an electrolyte. 3 main electrolytes of your body: Sodium (Na+), Chloride (Cl-), and Potassium (K+). Sodium and Chloride counteract each other to make a base... which is why one of the most common IV fluids in medicine is Sodium Chloride (same thing with eye wash... it's neutral). The two biggest factors in the fluid balance of your body is the Sodium and Potassium. Sodium retains fluid... it sucks the fluid in leaving the particles of the fluid left out. Ever get thirsty when eating salty foods, or popcorn at the movies? Salt is sucking the water in, making you thirstier. Sodium is a positive ion (hence the Na+), and positive ions attract water molecules.

Your kidneys also have a huge factor in fluid balance. Fluid balance is also called osmosis. If your kidneys aren't filtering your blood into urine properly, then you could retain fluid... thus causing edema. Do you urinate less?

Another is a hormonal imbalance. Aldosterone and Cortisol counteract each other. They are both steroid hormones produced by your adrenal glands. Aldosterone regulates Sodium and Potassium. An imbalance in them will certainly throw off Sodium levels, which in turn can cause fluid retention. However, your pituitary gland stimulates the Thyroid gland to stimulate the adrenal glands. You could have a pituitary, thyroid, or adrenal issue if you have an imbalance with hormones!

The very last thing I can think of is low protein levels in the blood. Proteins help keep the fluid in the bloodstream. If you have a low protein level in your blood (called Total Solids or Total Protein), then you aren't retaining fluid the way you'd like in your blood stream and it goes into your tissues causing edema. More specifically, Albumin (which is produced by your liver) can be super low. That is the MAIN chemical that keeps your blood in check. If your kidneys aren't functioning properly, Albumin can leak out through the tubing of the kidneys (where it SHOULD be retained in the blood) and is expelled in the urine.

In conclusion, ALL of this can be found in bloodwork. Electrolytes, kidney, liver, and TP values are part of a basic chemistry panel. The others would be an ACTH stim test, or Thyroid panel.

-Elevated Sodium
-Low Albumin
-Low Total Protein
-Overproduction of Aldosterone
-Underproduction of Cortisol
-Kidney failure/damage
-Liver failure/damage

Hope this helps!

I have had water retention issues all my life. I have brought it to the attention of my PCP but it never went further than watch sodium intake. I do watch my sodium intake, keeping it as close as possible to 2500 mgs or less. The other night I pressed in on my shin and the adema was so bad the impression was there well over 5 seconds.

Anyone else have this same issues?

your water retention can also be related to your obesity(no offense)

lose weight first then worry about water retention