Last summer I had an infestation of booklice in my apartment. By having a couple of slow leaks under sinks fixed, using dehumidifiers, boric acid, diatomaceous earth, and more patience than a person should be expected to have, I finally stopped seeing them. Now they've started showing back up. The whole time I have been keeping my humidity low, wiping up all the water left in the tub after showers, etc, etc. I should not have them again. But here they are. Maybe they are coming from other people's apartments, outside, or a leak in a wall? If there were a leak in one of the walls (the only place I can think of there possibly being one is the wall that the showerhead/bathtub plumbing is in,) wouldn't I be able to tell? I have powders under both sinks so that I know when there is a leak as it leaves a drip mark. They are not leaking.

Thanks for any advice.