I think we worry too much about the effects of spiro as a potassium sparing diuretic. Some of the people that have issues I have noticed have also have upped their water intake as they are worried about the diuretic effect and they wonder why they pee so much! Something else to consider is that estrogen shrinks your bladder over time too.
As for potassium, If you're not eating those salt substitutes then you generally don't have much to worry about. Otherwise you would need to avoid most plant foods which tend to be relatively high in potassium - like tomatoes, raisins, saltanas, potato chips, nuts, seeds, beans, bannanas, Not to mention meat and cheese and sea foods which are often high in potassium too. The amount you get from food is nothing compared to what you would get from a 'low' salt. And you should be getting blood checks now and then anyway which will pick up if you have too much potassium.