The most common source of water odor is dissolved organic matter. This can come from decaying leaves, algae, or even sewage. In some cases, this dissolved organic matter can give water a musty smell. Other potential causes of smelly water include chlorine, metals like iron and manganese, or sulfates. These contaminants can produce smells like rotten eggs, fish, or metal. If your water smells bad, it's important to have it tested by a professional.