Pain in Flank :

The flank is the lower back and side between the ribs and the hips. Flank pain can be constant or can come and go. It can be sudden and severe. It can be a sign of a urinary stone or a urinary tract infection. Contact your doctor soon if you feel strong flank pain or immediately if the pain is severe and/or includes fever.

For flank pain without accident, reduce/ decrease water intake for ureteric stone treatment.

It is old myth , if you drink more water, more will be chances of stone expulsion.... it is proved that is wrong.

Flank pain can also be a sign of a kidney injury. Injury can be caused by a car or bicycle accident, a fall, or a direct blow to the flank or abdomen during sports activities. Kidney injuries can also be associated with skin injuries or bruises (hematomas) in the flank area. In case of flank pain after an accident, see a doctor immediately.