Potential water quality issues

In 2016, the US Environmental Protection Agency published Technologies for legionella control in premise plumbing systems: scientific literature review. We extract the sections that are relevant for plumbers in relation to the prevention of legionella.

Chlorine can react with organics, inorganics and non-halogens in the water to form DBPs (disinfection by-products) (USEPA, 2006b).

Some DBPs have been shown to cause cancer and reproductive effects in lab animals and may cause bladder cancer and reproductive effects in humans (USEPA, 2010). In a simulated premise plumbing system of pipe loops, Loret et al. (2005) found trihalomethane (THM) levels >100 micrograms per litre (µg/L), with an applied chlorine dose of 2mg/L. For comparison, the EPA drinking water standard for total THM (TTHM) is 80µg/L. Orsi et al. (2014) noted that special equipment was needed in certain health care settings (for example, dialysis and neonatal care) to reduce free chlorine and THM levels.

Some DBPs are likely to be carcinogenic to humans by all routes of exposure, while others have suggestive evidence of carcinogenicity (NTP, 2006; USEPA, 2005a). For more information about THMs and potential health effects, see the EPA’s health criteria document for brominated THMs (USEPA, 2005a).

Continuous chlorination at high levels in premise plumbing systems can result in objectionable tastes and odours along with irritation of skin, eyes, and mucous membranes.

Continuous chlorination can contribute to corrosion, with associated leaks, in plumbing systems and may require the simultaneous use of corrosion-inhibiting chemicals. Various corrosion effects have been reported for systems using chlorination:

  • Sarver etal. (2011)reported that continuous hyperchlorination increased leaks byup to 30-fold, consistent with extensivelaboratorywrkin soft higher-pH waters.
  • Castagnetti et al. (2011)found that no high-densitypolyethylene (HDPE)pipe failure occurred after2 000 hours of exposureto 2.5mg/Lchlrine.
  • Hassinen et al. (2004)studied corrosion in HDPEpipe exposed to chlorinated water(3mg/L) atelevated temperatures (105°C, or221°F)and found evidencef polymerdegradation on theunprotected innerwalls ofthepipe.
  • Loret et al. (2005)observed similar corrosion marks on mild and galvanised steel coupons installed in pipeloops forvarious treatment chemicals (chlorine, monochloramine, chlorinedioxide, CSIand ozone).
  • Kirmeyer et al. (2004) reported that higher copper corrosion rates are associated with free chlorine compared to equivalent levels of chloramine; however, this is a site-specific issue.
  • In a study by Grosserode et al. (1993), leaks first appeared in the copper pipes of a premise plumbing system about two years after installation of the chlorine injectors. Significant deterioration was noted only in the hot water system. The addition of silicate corrosion inhibitors reduced the total number of leaks per year by >80%.

Operational conditions

Parameter conditions indicating operational effectiveness

The efficacy of chlorination is affected by many factors, including chlorine concentration, contact time, pH, temperature, turbidity, buffering capacity of the water, concentration of organic matter, iron, and the number and types of microorganisms in the water system (in biofilms and free-living). Lin et al. (2002) reported that 2–6mg/L of chlorine was needed for continuous control of legionella in water systems. The bactericidal action of the chlorine is enhanced at higher temperatures and at lower pH levels. The anti-microbial efficacy of chlorine declines as pH increases >7, with significant loss of efficacy at pH >8. However, free chlorine is degraded rapidly at elevated water temperatures, which is a concern for hot water chlorination (Health Protection Surveillance Centre, 2009). Turbidity interferes with the disinfection process by providing protection for organisms; turbidity may need to be reduced prior to disinfection (WHO, 2011b).

Installation considerations

Chlorine should be stored in the original shipping containers or compatible containers and sited away from direct sunlight in a cool area. Feed rates should be regularly adjusted to account for any losses in chlorine content during storage or handling.

NSF/ANSI Standard 60 certification can help ensure that the quality and effectiveness of water treatment chemicals have been reviewed and found to be acceptable for potable water applications. Some primacy agencies require NSF/ANSI 60 certification. A facility considering application of chlorine gas as the form of chlorine to be used for disinfection would also need to consider potential safety and security concerns. Additional safety procedures will likely be required for personnel training and equipment. Existing OSHA, state or local fire authority regulations may apply and may need to be consulted. Special water system engineering construction standards may also apply for some primacy agencies.

Monitoring frequency and location

If a premise plumbing system is a regulated PWS, then the SWTR (USEPA, 1989a) requires that PWSs adding chlorine and using a surface water supply or a ground water supply under the direct influence of surface water monitor for the presence of the residual disinfectant in the distribution system or at the entry point to the distribution system (EP). The disinfectant level must be at least 0.2mg/L at the EP and detectable in at least 95% of samples collected within the distribution system.

The Stage 1 D/DBPR requires that PWSs that use chlorine maintain a residual disinfectant level of less than 4.0mg/L as a running annual average (USEPA, 1998).


“… maintenance of an appropriate disinfectant residual, regular system cleaning and flushing, inspections, and water quality monitoring.”


As stated in the SWTR, PWSs that use chlorine are required to monitor for combined or total chlorine residual or heterotrophic plate count (HPC) bacteria in the distribution system at locations that have been approved by the primacy agency (USEPA, 1989a). These parameters could provide operational information to indicate the need for chlorine dose adjustments, system flushing and managing water age within finished water storage facilities.

Maintenance needs

Operations and maintenance practices for chlorine disinfection systems include maintenance of an appropriate disinfectant residual, regular system cleaning and flushing, inspections, and water quality monitoring. Newly constructed or rehabilitated piping systems are cleaned and flushed prior to initial disinfection. Routine flushing and water quality monitoring are recommended to assure that adequate disinfectant levels are maintained throughout the premise plumbing system (HSE, 2014).

Since chlorine is recognised as being less effective than other disinfectants at penetrating and controlling established biofilms, chlorination may not be effective if large amounts of scale and sediment are present in the system. These solids are prone to biofilm formation and may need to be removed by cleaning before effective disinfection can be achieved (HSE, 2014). Loret et al. (2005) recommended flushing dead ends daily with disinfected water and removing premise plumbing fixtures and pipes that are rarely used.


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