What does it mean if you have water on the kidney?
"Water on the kidney" is the literal translation of the medical
term hydronephrosis. That's a misnomer, however, because the
condition has nothing to do with water. In hydronephrosis, there is
often an obstruction in the ureter, bladder, or urethra that
prevents urine from emptying out of the kidney. Pressure backs-up
as a result, causing the kidney to swell with urine.
A common cause is a large kidney stone that prevents proper
drainage of the kidney.