I know Lasix will deplete potassium levels, but I know that dandelion root is potassium sparing. It's pretty safe. Definitely not in the same league as Lasix or any other powerful diuretic drugs. I don't know about the other natural herbal or food diuretics, but I would imagine they're also quite safe.
Once a month should be fine. I did 24g of dandelion root for three days, along with some caffeine, alcohol (red wine), and reduced water and sodium intake. I felt fine aside from a very mild headache on the last day. This was a "contest prep" thing....no, I don't compete, but I wanted to experiment with it.
You could definitely eat the diuretic fruits and veggies on a regular basis if you wanted. Not sure how much of an effect that would have...maybe someone can try it and see if it does anything.