A slimy reddish-brown, orange, or grayish film in a toilet tank, on an outdoor hose bib, or around a faucet aerator is one of the more common things Missouri well owners notice. Often it is iron bacteria, a group of naturally occurring microorganisms that feed on dissolved iron and manganese and build up a gelatinous coating where water sits or moves slowly. This guide explains how to identify the film, how to narrow down where it is coming from, and what testing can and cannot tell you.
What the film is
Iron bacteria and related organisms leave a slick, sometimes stringy coating that often looks rust-colored. It feels slippery when rubbed between your fingers and may carry a faint earthy or musty odor. Wiping it away usually brings it back within days or weeks if the water keeps supplying the same food source.
Rust from dissolved iron itself looks different. It tends to leave hard, flaky stains that wipe away poorly and often show up on white porcelain as orange rings. Slime is soft and regrows. Both can appear together, so pay attention to texture before deciding which one you are dealing with.
Where to look first
Start at the places where water sits or moves slowly:
- The walls of the toilet tank and the underside of the lid
- The outlet and inside of each outdoor hose bib
- Faucet aerators, which may show a rust-colored ring or a gelatinous plug
- The sediment drain on the water heater, if the film appears only in hot water
- Dead-end branches of the cold water system, such as an unused bathroom or a seldom-run outdoor line
Narrow down the source
Compare what you see across fixtures before drawing conclusions.
- If the film appears only in hot water, start with the water heater. Check whether the sediment drain carries similar material, and note whether the cold line at the same fixture is clear.
- If the film appears in cold water at toilets and outdoor spigots but not at kitchen taps that run often, the film may be settling in low-flow areas. Frequent use of those fixtures can keep the film from building up.
- If the film appears everywhere, including fixtures used daily, look at the well house and the pressure tank area for signs of staining or slime on fittings and drains, and make a note of what you find.
Keep a short written record of which fixtures show the film, how often you see it, and whether it returns after cleaning. That record will help anyone who tests or inspects the system later.
What testing can tell you
Testing is the only way to know what is actually in your water. A certified laboratory can analyze a sample for total coliform and E. coli bacteria, and it can measure iron, manganese, and other dissolved minerals. Iron bacteria are not usually part of a routine bacteria test, so a clean coliform result does not explain the slime by itself. Ask the lab whether it offers a test specifically for iron bacteria, and follow its instructions for collecting and shipping the sample. Do not use a household container unless the lab tells you it is acceptable.
A test result tells you what was present on the day the sample was taken. It does not confirm that the water will remain the same, and it does not tell you whether the film is harmless in every situation. If a test shows bacteria that should not be there, follow the lab's guidance and contact a qualified water professional or your local health authority.
Cleaning and what to avoid
Scrubbing a toilet tank or aerator removes the film for a while, but it will likely return if the water supply has not changed. Use only cleaners listed for your fixtures, follow the label directions, and never mix cleaning products together. Ventilate the room while you work.
Treating the well itself with an oxidizer or disinfectant is a different job. It requires knowledge of your well construction, your pump, and your plumbing, and it should be handled by a qualified professional. Any treatment should be followed by the post-treatment testing timeline your provider recommends.
When to get help
Contact a qualified water professional or your local health authority if the film returns quickly after cleaning, if the water has an unusual odor or color that is new, if the lab reports bacteria, or if you notice changes in water pressure or flow along with the film. A well professional can inspect the well house, pressure tank, and plumbing, and can explain what options exist for your specific system.