I used to have quite a lot of problems with my kidneys a few years ago (I am just 25 y.o.). I was born with kindneys displacement which sometimes caused blockage of urine resulting in inflammations. I was once diagnosed with two micro size kidney stones which caused a lot of discomfort, but they were so small that I passed them without even knowing that.

Half a year ago I started to use only Sea Salt in my cooking as well as I did cut on all ready made foods with preservatives . I did not have any problems with my kidneys since than.

Tonight I am doing kidney clense with watermelon. I don't think I have any stones there, but I have a little heavy feeling in my lower back so I decided to do the clense. I'll though check my urine, at least visually, if there is anything special there.

Some discussions about the Watermelon clense you can find on this page.
I only have to add, that according to my source of information, the most important part is to eat the Watermelon between 2 and 3 o'clock night time. Because this is the best time when kidneys can pass stones or sand. And if you really have stone or send there you better sit this hour or two in a bath tub. I believe it will be much better in a nice warm water, it will relax and open the urinary tract and the stones or sand would smoothly go out with less pain.
I've seen people passing stones in a hospital, no bath tub, no watermelons. I know how painful it may be.

Good health to you!