Why Do I Have Red Residue from Water?

Iron takes two different forms in water: soluble ferrous iron and insoluble ferric iron. Both types cause red water stains, but it’s important to identify which type you have because each requires a different solution.

Soluble ferrous iron in water is invisible to the naked eye when fresh out of the tap. However, when the ferrous iron is exposed to the oxygen in the air for a long time, a chemical reaction occurs that turns the iron a rusty red color. This reaction also causes iron bacteria to grow, which have a red, slimy appearance. The surrounding surfaces are stained red as a result.

Unlike soluble ferrous iron, you can see insoluble ferric iron floating in your glass of water. This type of iron has already been exposed to oxygen, which turns it red. As a result, your water will have a rusty red appearance when you pour it from your tap.

As we mentioned above, Serratia marcescens bacteria occur naturally and travel through the air to high-moisture environments. The standing water in a toilet bowl or leftover puddles in a tub after bathing are particularly vulnerable to Serratia marcescens infiltration.

Serratia marcescens growth is especially likely in water that does not have chlorine in it. Filtering chlorine out of the water in your home is essential to protect your health. However, chlorine also helps protect standing water from bacteria like Serratia marcescens. So, the stains caused by these bacteria are an unfortunate side effect of dechlorinating your water. But we think having to clean these stains is better than dealing with the harsh health effects that drinking or bathing in chlorinated water can cause.

So, are those red stains in your shower stall caused by iron or Serratia marcescens? There are a few ways to distinguish between the two. One is the color of the stains. Iron stains tend to be on the darker red or orangish side, while Serratia marcescens stains are usually pinker.

Another factor to pay attention to is if the stains are more constant or tend to come and go. Serratia marcescens stains tend to come and go because the bacteria often infiltrate the home after certain events. For example, they can get in during the summer months when the windows are open or after construction or home renovation projects that stir up dirt and dust. Iron stains, in contrast, tend to be more constant because of steady iron contamination year-round.

Paying attention to the above factors will give you a hint at what you’re dealing with. The only way to know for sure is to get your water tested. We’ll discuss water testing in more detail below.