damn! just get one of these: http://www.discount-pumps.biz/WA-55LV.jpg, set it under the waterline of your tank, attach an air tube to the output part, run the tube up to your waterfall, cover the end of the tube with some rocks, plug it in, adjust the flow, and vuala!
depending on the filter you get it could cost you as little as 10 dollars, these are all some pretty good ideas though.... what size tank are you using it for?