Concentrations of ammonia in rivers and drinking water reservoirs indicate the presence of agriculture or urban pollution. When the concentration of ammonia is high, it can alter the smell and taste of water. In industrial applications, high concentrations of ammonia can cause corrosion in pipes. Ammonia is also monitored in aquariums and fish farming applications because of its toxicity to fish.

The HANNA ammonia portable test kit determines the ammonia concentration in water in several easy steps. The ammonia level in mg/L (or ppm), ammonia as nitrogen is determined by a colorimetric method. The Nessler reagent reacts with ammonia, under strong alkaline conditions, to form a yellow colored complex (see equation below). An addition of Reagent 1 for Sea Water inhibits precipitation of calcium and magnesium ions due to the presence of the alkaline Nessler reagent. The color intensity of the solution determines the ammonia concentration:

2K₂Hgl₄ +2NH₃ → NH₂Hg₂I₃ + NH₄I + 4KI