Anhydrous ammonia is ammonia in its pure form, with no water present. Ammonia on the other hand, is the chemical compound NH3, which contains one nitrogen atom and three hydrogen atoms, and always has water present in it, usually in the form of ammonium hydroxide (NH4OH). The difference between the two is the water content, anhydrous ammonia is ammonia without water while ammonia is ammonia with water. The major differece is in the purity of ammonia, in case of anhydrous ammonia is 99% pure amd household ammonia is 10-15% pure.