This seems logical since the iron in the water comes out of solution through an oxidizing process that increases as it travels through warm air. Under these conditions, the iron is already precipitated out of the water by the time it hits the leaf surface and is deposited there. If the conditions are such, as in most years, so that it does not precipitate out in mid-flight then it merely hits the leaf and then falls to the ground where the iron eventually comes out of solution. Even if the water contains 1.5 ppm, then only about 2.5 pounds per acre is applied per year, which isn t harmful at all. Recommendations for removing iron from water are to allow it to aerate in a holding pond or by ejecting chlorine in conjunction with an irrigation filter.
Chlorine acts as a catalyst to instantly precipitate iron which then can be captured in a filter.
The University of Missouri can run water tests in their Columbia lab. If you think that you have a problem with excessive iron levels call the Delta Center for more information.