Hmm so if it washes contaminants down hill, much like rain does, here's my suggestion: make sure your water isn't acidic, because some rain is acidic from the burning of fossil fuels, and acid rain is bad. Add pothos to ur tanks to soak up all nitrates so all that you'll be changing is water with very little waste in it, heck u might actually negate the need for huge amounts of wc with an equally huge amount of pothos. And lastly, but most importantly, make sure to create a huge mountain chain up wind of your location to break up the natural cycle of rain in your location and to create a desert where no rain or running water will ever get a chance to wash off surface contaminants your neighbors will now have an oasis of dog and other animal poop all over their property but at least the world is saved!!! Just my $.02 lolIt's not from my pond. I never do WC on the pond. It's from my tanks. Maybe able 100g total out the garage door. Because the property is sloped there is no flat area for the water to be absorbed. The water runs downhill about 100 feet, enough for PITA neighbors to notice. It does not reach any street drains but their point is it washes accumilated contaminants down hill.