Summary of Slime Forming Bacteria (from the KnowYourH2O Website)

Slime bacteria (also called slime-forming bacteria) are a group of non-pathogenic nuisance microorganisms that produce a sticky biofilm or slime. Unlike iron-reducing bacteria, they do not require iron or manganese to grow.

What They Are

The slime is typically gray or clear and thicker than iron-bacteria slime. It can turn yellow or beige if metals accumulate in the polysaccharide layer. The slime layer becomes thicker when the bacteria are stressed or under aerobic (oxygen-rich) conditions.

Problems They Cause

These bacteria create nuisance issues by:

• Interfering with disinfection systems and other water treatment systems or water related systems.
• Causing microbiologically induced corrosion
• Reducing the performance of water appliances, filters, and ion-exchange systems
• Masking the presence of coliform bacteria or other waterborne pathogens

They can lead to premature failure of treatment devices and, in severe cases, elevate levels of copper, lead, zinc, and other corrosion by-products in the water.

Health Risks & Standards

No specific health risks from slime-forming bacteria themselves are known. Abundant growth mainly creates aesthetic problems (taste, odor, feel) and operational issues.

There are no dedicated numerical standards for slime bacteria. They fall under the broader heterotrophic (“standard plate”) count standard (< 500 colonies per mL) and the total coliform rule (absent). A high plate count does not automatically mean slime bacteria are present.

Warning Signs & Testing

Level 1 – Observational self-testing

• Slimy coating or feel on the inside of toilet tanks, pipes, filters, appliance surfaces, or water tanks
• Biofilms that look clear, white, gray, yellow, beige, or lightly discolored
• Off-taste or slight odor; in extreme cases the water may pour more like a gel
• Signs of corrosion (blue-green water, pinhole leaks, clogged pipes with slimy debris)
• Increasing chlorine or oxidizer demand if the water is being disinfected

A simple home check: rinse a clean jar, fill it with the water, leave it in the dark for 1–2 weeks, and look for slimy growth.

Level 2 – DIY / laboratory testing: BART kits that specifically detect slime-forming bacteria (often sold in combination packages that also check iron-related and sulfate-reducing bacteria) are recommended. Other useful kits include general drinking-water test panels and Legionella filtered-water tests. Shock disinfection is often advised before additional testing if bacteria are confirmed.

Seeing slime or biofilm in your water system? The Bacteria Problem Suspected Kit tests for slime-forming and other nuisance bacteria — a smart first step before choosing a treatment system.

Treatment Recommendations

Short-term

• Inspect the wellhead.
• Perform shock disinfection of the well and distribution system twice, with all treatment systems bypassed and in-line filters/aerators removed.
• Flush the lines thoroughly.
• Pasteurize the water heater and hot-water lines (raise temperature above 140°F / 60°C for several hours, then flush carefully to avoid scalding).
• For municipal (city) water: flush the main if possible and install a clear filter housing right after the water enters the home.
• You may want to check the disinfection residual of the water and the oxidation reduction potential (ORP).

Long-term: Ongoing control typically requires chemical oxidation/disinfection combined with particle filtration. Professional system design and regular maintenance are usually necessary. The underlying problem may be natural and may require periodic well cleaning or rehabilitation.

The page lists specific product recommendations (BART combination kits, Well-Safe shock kits, sanitary well caps, chemical injection systems, whole-house filters, related books, and additional test kits) and stresses working with local professionals for lasting solutions.

Bottom line: Slime bacteria are a common cause of clear-to-gray sticky biofilms, off tastes/odors, and reduced system performance. They are primarily a nuisance and corrosion concern rather than a direct health hazard. Shock chlorination plus heater pasteurization is the usual first step, followed by ongoing disinfection and filtration when needed.

Want to learn more about your water? Our Drinking Water Guide for Well Water and City Water is an educational booklet covering water quality issues, testing, and treatment options for both private wells and municipal systems.

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