Oh and even in retention ponds you can soak the roots and change the water several times to make them edible. I would call this a last resort and concentrat on a water source that has at least some natural motion to it. but in desperate times you can soak and change water a half a dozen times and the cattail root will release the majority of the crap it can soak up. Its one of the good things about cattails. they dont want to hold toxins or heavy metals in the roots. But like i said. last resort.
