What is Iron?

Iron is a metal element that is found naturally in the ground. It is also a key component in our blood.

Iron is the most common problematic mineral in groundwater sources around New Zealand.

While iron is not dangerous, it certainly can be a nuisance.

The New Zealand Drinking Water standards set a guideline value of 0.2mg/L or less for staining, taste and smell.

How does Iron get into my water supply?

When water comes into contact with iron-containing rock in the ground (like Hematite), iron dissolves into the water.

What does Iron do?

When water comes from the ground and hits the air, the iron oxidises from Fe 2+ to Fe3+. Oxidised iron is also known as rust. This will stain everything it comes into contact with, often a red/brown or yellow colour depending on the level present.

It also blocks pipes and fixtures and encourages the growth of bacteria.

It feels drying and irritating on the skin.

So while the iron is not dangerous and is even beneficial to us, drinking water is not the place we want to be getting it from.

I have heard of different types of iron, what does that mean?

There are 5 different types of iron. This is important to us as what type of iron you have can affect how we treat your water.

Dissolved/Ferrous Iron

This type is most common in groundwater before it is exposed to air. It takes the form Fe2+. This water looks clear when discharged, but if left for example in a bucket it will turn brown. This cannot be filtered, but it can be removed by other means (e.g. cation exchange)

Oxidised/Ferric Iron (Rust)

This is common when the water has been exposed to air (e.g. in storage tanks). It takes the form Fe3+. This is a precipitate or suspended particles in the water, it is no longer dissolved. It can now be filtered. The water often has a red/brown appearance.

Colloidal Iron

Is in essence the same as Ferric iron (Also Fe3+), but the particles have formed at less than 1 micron in size, making them more difficult to filter. A coagulent may be needed

Organically Bound Iron

When tannins are also present in groundwater supplies, they can bind with ferrous iron, making it more difficult to remove. If softening is used it may need to be combined with tannin removal to be effective. Otherwise, oxidation and filtration can be used.

Bacterial Iron

There are several species of iron oxidising bacteria which can infect wells. These colonise the surface where water from an anaerobic environment meets the aerobic environment. These bacteria feed on soluble/ferrous iron and oxidise it to ferric iron Mucous is produced in the process and this often appears as a brown slime.Oily films may be observed on the water surface and a smell may be noted resembling fuel or sewage.

Iron bacteria are difficult to deal with once they are established. Shock treatment of wells with chlorine can be effective, however this may need to be repeated regularly. Otherwise continuous oxidation/filtration is an effective method of control.