Tiny organisms can cause big problems

In this month’s column, I’ll discuss a situation that can happen frequently, have a large financial price tag for property owners and require extensive work to remedy. This scenario and its resolution may provide water treatment specialists with a window on how quickly treatment systems can be compromised and why a trained professional is the key to making sure systems are well-maintained and operating at peak efficiency.

How it started

The rental property home was a lucrative investment for the client; he derived as much as $10,000 (USD) per night renting the home to skiers in an exclusive mountain resort town. He retained the services of a professional property management company to ensure the home was always ready for paying customers. During a routine off-season maintenance visit, the property manager was exercising the faucets and fixtures and discovered a pink slimy residue at the water level in one toilet, as well as a black slimy residue in the toilet tank of another. He’d seen this kind of thing before in vacation homes that are unoccupied for extended lengths of time. The property manager added a chlorine tablet to the tank and left the home. He visited the home again a week later and found the same black residue in each of the home’s seven toilet tanks and also noticed a ’swampy‘ odor when he ran water at any of the home’s showers. At this point, the property manager realized that he needed professional help.

A WQA-certified water specialist (CWS) was called. He arrived at the property determined to help discover the source of the problem and hopefully provide a solution. The CWS looked at the situation holistically and observed the following items of interest:

  • The pink slime appeared to be S. Marcescens.
  • The water softener was large enough to accommodate the high flow rates required for the home, but programmed only to regenerate when the capacity was exhausted, which could be daily during peak season, or every 90 days during slow season.
  • There was a strong organic odor in the brine tank.
  • Both clothes washers smelled musty and swampy.
  • The under counter commercial icemaker exhibited clear evidence of bacterial contamination.
  • Translucent Wirsbo PEX tubing to and from the home’s central RO processor showed clear evidence of black biofilm accumulation.
  • A slimy black residue was colonizing all of the toilet tanks, in spite of the chlorine tablets added by the property manager.
  • Humidifier evaporator pads showed clear evidence of bacterial accumulation.

This was a serious situation indeed. Biofilm accumulation in pipes, faucets, fixtures and water quality management devices can create unwelcome tastes and odors in water, and potentially even harbor dangerous pathogenic organisms. The CWS recommended decisive measures to ensure protection of future guests who would visit the property. His first order was to immediately prohibit further occupation of the home until the problem was satisfactorily resolved.

The CWS implemented a proven, yet simple treatment regimen. As with all disinfection procedures, he was careful to document all work in writing and photographically.

Perform plate culture testing to establish a baseline of the extent of contamination. An agar pour plate test was performed. Heterotrophic plate count (HPC) bacteria levels were ‘off the chart’, fully occupying the entire dish. A coliform test was also performed, which thankfully indicated negative for E.coli. and fecal coliforms. Had either test result been positive, the CWS would also have notified the appropriate local authorities to be fully compliant with local regulations and city ordinances.

Identify and remove all possible sources of contamination. The prime suspect in this debacle was a 20-inch Big Blue profile sediment filter. The filter housing was an off-brand model sourced from a regional discount OEM and the cartridge was of unknown provenance. Prefilter and RO cartridges were replaced six months earlier by an inexperienced handyman and the property manager was uncertain about whether sanitary handling procedures were actually followed. The filter housing was opened and the contents smelled like sewage! Evidently, there was a massive bacterial colonization in this housing and cartridge, most likely the source of all other living organisms passing into the home.

The CWS determined that the cartridge and housing should be removed outright. Simply up-sizing the softener venturi assembly negated the need for sediment pre-filter on this municipally supplied water. During removal of the housing, it became evident that piping upstream of the housing was clear of contamination and odors, while downstream piping contained an odiferous slimy residue.

Isolate contaminated appliances, and disinfect or replace as prudent. The water softener was carefully examined and determined to be unsalvageable. A new softener was installed by a local licensed plumber, then fully sanitized to ensure that it couldn’t further contribute to contamination issues. It incorporated an automatic disinfection apparatus as well as fractional brining software to allow for frequent cleanings without wasting salt.  The existing RO processor was opened and evaluated to ascertain the level of contamination. The filter cartridges were clearly contaminated and, after a careful examination of the housings and manifold, it was determined that the entire apparatus should also be replaced.  Toilets were drained and physically scrubbed with detergent to remove all physical adhesions. Once those were removed, toilets were sprayed with an organosilane quaternary amine disinfectant and completely air dried before being returned to service. Toilet flappers and floats were replaced with chlorine-resistant materials, and a chlorine/bromine dosage regimen was prescribed. All toilets were effectively disinfected and exhibited no signs of regrowth after 12 months. Washing machines were carefully cleaned and disinfected using concentrated detergents, hydrogen peroxide, and quaternary amines. All humidifier pads were discarded, the sumps were sanitized and all associated tubing replaced.  Two of the under counter icemakers were satisfactorily disinfected, but the third was so severely contaminated that it was recommended to be replaced outright.

Disinfect all piping, faucets, and fixtures, replacing components as necessary. Disinfecting the piping proved to be quite challenging because the 18,000-square-foot home contained a large amount of copper and PEX piping as well as numerous faucets and fixtures.  The first step was to drain down the entire plumbing system and turn off the humidifiers for a week to allow the piping to dry out and allow the biofilm to begin collapsing. With a solid understanding of the capacity of different pluming materials to harbor bacteria, the CWS targeted the PEX tubing first and had a local licensed plumber replace all accessible tubing that showed evidence of contamination. Once all visibly contaminated tubing was replaced, the entire plumbing system was flushed with a phosphoric acid solution, then filled with a water-based solution of anionic, cationic and non-ionic surfactants to help loosen any existing biofilm. This detergent solution was circulated from the furthest point in the home back to the main water inlet using a diaphragmatic pump and flexible tubing. After 24 hours of contact time, the detergent solution was flushed from the piping along with residual biomass that was released. The entire system was again flushed with clean, soft water and then drained down again to dry for a further 48 hours. After drying, the piping was further disinfected with a sodium hypochlorite (10-percent chlorine) solution that was circulated and then allowed to dwell for one hour before rinsing. All showerheads and faucet aerators were removed, physically inspected and sanitized/replaced as appropriate. After rinsing again, tests were performed to ensure no detergent or disinfectant residuals remained in the product water.

Perform supplemental testing to confirm efficacy of disinfection. Supplemental plate cultures were performed 24 hours after the disinfection was completed. After sufficient incubation time, the agar pour plate test method indicated a negligible level of HPC.

Perform additional disinfection/remediation as necessary. Based on the successful test results, no further disinfection was deemed necessary. The CWS retested at six- and 12-month intervals subsequent to disinfection to confirm the efficacy of the solution. Each time, the plate culture results were below recommended levels.

Implement a scheduled cleaning and disinfection plan to prevent future contamination. Due to the seasonal nature of occupancy at this home, it was decided to perform periodic cleaning and disinfection as well as RO filter changes at the home bi-annually to ensure that each peak occupancy season began and ended safely.


Many lessons can be learned from this incident, most important being that water quality management devices should only be installed and maintained by qualified professionals. Another lesson learned is that municipal chlorination can’t protect from all bacteria all the time. Biofilm can accumulate at any time. Be ever vigilant to this silent menace and take appropriate preventative action. Never underestimate the power of tiny organisms.

Glossary of terms

HPC – Heterotrophic Plate Count. A heterotrophic plate count is a catch-all test for general bacterial growth; HPC testing doesn’t generally identify specific strains of bacteria. HPC testing has a long history of use in water microbiology. HPC tests can be used as indicators of the proper functioning of treatment processes and indirect indicators of water safety.

COLIFORM – The name of a test adopted in 1914 by the US Public Health Service for the Enterobacteriaceae family. This test is a commonly used bacterial indicator of sanitary quality of foods and water. The term coliform refers generally to bacteria in this group. They are defined as rod-shaped, Gram-negative, non-spore forming organisms.

E. COLI – Escherichia coli, a gram negative rod-shaped bacterium commonly found in the lower intestine of warm-blooded organisms. Most strains are benign, but some, such as serotype O157:H7, can cause serious food poisoning in humans. Presence of E. coli in water is commonly interpreted to indicate fecal contamination.

SURFACTANT – Natural and synthetic compounds that lower the surface tension of a liquid, allowing easier spreading, and lowering of the interfacial tension between two liquids, or between a liquid and a solid. Surfactants may act as: detergents, dispersants, wetting agents, foaming agents, and emulsifiers.

S. MARSCESCENSSerratia marcescens, an antibiotic-resistant, gram-negative bacteria in the enterobacteriacea family. This bacterium is commonly found growing in shower stalls, showerheads, and toilets in homes. Certain urinary tract infections as well as respiratory disorders have been associated with this bacterium.