If you need a pump for potable (drinking) water, you must use a bronze pump. With a bronze pump, you absolutely need bronze flanges. Cast iron flanges will rust, compromising your whole system. With a cast iron pump, you can use either bronze flanges or cast iron flanges. With no clear benefit of using bronze flanges with a cast iron pump, most people opt to save some money and use cast iron flanges.
Taco pumps and flanges can be found at www.supplyhouse.com
