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The objective of this work was to demonstrate the effectiveness of a simple and innovative biological water treatment approach for removing 3.3 mg nitrogen (N) per litre of ammonia and iron from water using a pilot study conducted at a utility in Iowa. Biological water treatment can be an effective approach to addressing low ammonia levels; however, providing adequate oxygen to address source water ammonia levels greater than 1.5 mg/L N is challenging. The treatment consisted of a biological "contactor" combined with aeration, followed in series with a dual granular media filter. Orthophosphate was necessary to satisfy biological nutrient requirements, and maintaining near-saturated dissolved oxygen levels throughout the contactor was important. Many regions across the United States have elevated levels of ammonia in their groundwater as a result of natural and agricultural sources. Although ammonia in drinking water does not pose a direct health concern, nitrification (i.e., the conversion of ammonia to nitrite and nitrate by bacteria in the presence of oxygen) of ammonia in the drinking water distribution system may.