I have had success with the combo Iodine and borax for various urination problems, like to frequent, enuresis in kids etc. Works fast.
As trapper says, salt is important, so are magnesium (some cases of frequent urination may have a cramping element due to magnesium deficiency, thats where the boron comes in)
My own son (now 15) had frequent urination badly from he was little; had to urinate up to 15-20 times a day, just dribbling each time. He was also up 2-3 times a night when he was 12.
All gone now, completely cured;
Iodine, companions + extra emphasis on boron - magnesium.