The presence of iron in ground water is a direct result of its natural existence in underground rock formations and precipitation water that infiltrates through these formations. As the water moves through the rocks some of the iron dissolves and accumulates in aquifers which serve as a source for ground water.

Since the earth's underground rock formations contain about 5% iron it is common to find iron in many geographical areas around the globe.

Iron in water is typically found in three major forms and is rarely found in concentrations greater than 10 milligrams per litre or parts per million (mg/l or ppm):

• ‘Clear water iron’ is a non-visible ferrous (Fe2+) form of dissolved iron is found in water that is not exposed to oxygen, such as in wells and springs.

• ‘Iron bacteria’ – Dissolved iron contributes greatly to the growth of iron bacteria. These bacteria form dark-coloured slime layers on the inner walls of the system's pipes.