Iron can be water soluble or water insoluble depending on the ionic state of iron and the compounds that it forms. Following the general solubility rules, iron is soluble when bonded to certain polyatomic ions such as sulfate and nitrate as well as halides like chlorine and bromine.
The ionic state of iron can affect whether the compound dissociates in water and becomes water soluble. For example, Iron II is soluble when bonded to oxalate, but Iron III is insoluble when bonded with the same polyatomic ion. Likewise, Iron III Ferricyanide is water soluble but Iron II Ferricyanide is not. Iron II and Iron III have charges charge of +2 and +3 respectively which causes them to be needed in different proportions in ionic bonds.
Iron is a trace mineral that can be found in certain types of foods and is needed for specific biological processes in the human body. Too much iron can be toxic though, so iron levels in the body should be watched accordingly. Besides food, soluble iron can also be found in water that has passed through certain pipes or has been taken out of geological sources such as ground wells. The effects of iron in drinking water can range from negligible to somewhat detrimental and can be treated using a variety of techniques.