What is the role aldosterone in sodium and water balance?

Answer 1

"Aldosterone acts on the tubules (i.e. the distal convoluted tubules and the cortical collecting ducts) in the kidneys, causing them to reabsorb more sodium and water from the urine."

Sorry to quote verbatim, but sometimes there isn't a better way to say it. I've included a Wiki link for the Renion-Angiotensin System in the source list below.

Good luck.

P.S. Aldosterone also acts on the collecting duct: "...stimulates H+ secretion by principal cells in the collecting duct, regulating plasma bicarbonate (HCO3−) levels and its acid/base balance"

If you like to study blood gases, this is important info... but is not specific to your question.