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Health Risks Related to Microbial Growth and Biofilms in Water Distribution Systems

A biofilm is a slimy, glue-like substance excreted by bacteria which are adhering to a surface in a watery environment. These organisms including viruses, protozoa, invertebrates, algae, and fungi, which can survive and grow in the water distribution system, may cause disease in healthy people or in individuals who are sick or immunocompromised. Their metabolic products such as toxins produced may also cause disease.

Microorganisms can also induce corrosion of the pipes, reduce the effectiveness of indicator organisms which would show where there is contamination present, produce taste, color and odor problems, react with the disinfectants to reduce the available dose for control of microorganisms, and produce disinfectant byproducts.

Microorganisms enter the water distribution system because of: raw water problems; breaks in treatment plant techniques; cross-connections and backflow problems; contamination of finished water storage; trespassing and lack of proper security of the water system; etc. The microorganisms can grow because of the presence of nutrients and the slowing down of the water through the system, which also allows for disinfectant residual to be below standard. The accumulation of sediment in the lines also contributes to bacterial growth.

Best Practices for Water Distribution System

  • • Use tracer studies to determine water quality and water age by measuring the amount of chlorine residual or trihalomethanes. The tracers can be injected chemicals like fluoride or calcium chloride.
  • • Use the appropriate American Water Works Association standards for designing a water distribution system for the community. The distribution system must also meet the fire protection needs and all state regulations.
  • • Do not close off distribution system valves because this will result in a dead end which may contribute to contamination of the water when the valve is reopened.
  • • Maintain a minimum pressure of 20 pounds per square inch at all locations at all times in the water distribution system.
  • • Ensure that all water which is stored will be mixed to avoid stratification.
  • • Use water system flushing as a means of removing sediment and stagnant water from the distribution system.
  • • Make sure that the drinking water treatment plant is working effectively to remove organic matter and organic chemicals to avoid later biochemical stability problems in the distribution system.
  • • Use frequent testing and monitoring techniques to determine elevated disinfection byproducts (DBPs), lower disinfectant residuals, increased bacterial counts, and increased nitrate/ nitrate levels. All of these indicate aged water and other problems.
  • • Assess the potential for infrastructure problems by accumulating information from the past and mapping the entire water delivery system. Determine the frequency of complaints by location, frequency of breaks in the lines by location, the adequacy of provision of proper quantities of water of high quality, and the adequacy of water needed to fight fires. Place on the map those areas which are most prone to problems and immediately provide a maintenance and replacement program to keep from having larger problems later.
  • • Develop a present and future pipe replacement program based on facts and determine in advance necessary means of financing.
  • • Pipe failures can be reduced or eliminated based on the specific types of problems encountered by: higher operating pressures for pressure problems; surge control and operator training for hydraulic transients; cleaning and lining the pipe for internal corrosion; cathodic protection (a technique to control corrosion of a metal surface underground) for external corrosion; replacing the joint only for leadite expansion or corrosion; installing dielectrics for material incompatibilities; and replacing the joint only for gasket deterioration.
  • • If a water main fails, the least expensive way to replace it is to use an open trench system where the new main is in a trench parallel to the old main and the old main is disconnected but left in place.
  • • Renew underground pipes by using non-structural, semi-structural, or structural lining techniques within the interior surface of the pipe depending on the particular situation, to restore the pipe’s integrity and ability to move the potable water through it without contamination. At times the pipes will have to be replaced, especially if the pipe has had structural loss of strength, lack of adequate flow capacity, and joint leaks that cannot be solved by other techniques, and the water quality problem cannot be resolved with insertions in the pipes.
  • • Detect suspected permeation and leaching problems by monitoring the water especially if newer rehabilitated mains, for total coliform bacteria, disinfectant byproducts, pH, disinfectant residuals, turbidity, and odor.
  • • Prevent permeation and leaching by using proper materials and installation practices when designing and installing replacement systems. Utilize the appropriate American Water Works Association manuals to help make decisions.
  • • Water mains must be separated from potential contamination including sewage pipes, stormwater pipes, or reclaimed wastewater pipes. There must be a 10-foot horizontal separation between the water mains and sanitary sewers and an 18-inch vertical separation for a water main crossing above or below a sewer. Where possible, all water mains should be above sewer lines.
  • • There must be on the potable water system adequate numbers and types of fire hydrants and valves, and the valves must provide for complete isolation of the potable water.
  • • There must be a minimum number and lengths of tie-ins to the water main.
  • • All existing water mains and service connections must have watertight caps or covers.
  • • All fittings, joints, and valves that have been exposed to the environment and hand tools, tapping machines, and other equipment that come in contact with pipes and fittings must be disinfected before being used.
  • • Remove any water from a trench so that it will not contaminate the pipes.
  • • Follow the appropriate American Water Works Association standards for installation and repair of pipes.
  • • Use the existing data concerning pressure differentials in different parts of the water distribution system to determine which portions are most likely to have low-pressure events and when. Establish a maintenance program that will deal with these problems and especially where leaks are occurring.
  • • Train personnel in the use of hydrant and valve operations, the proper use of hydrants, and what the potential problem may be in causing low-pressure events resulting in contamination and potential disease outbreaks.
  • • Controlling the growth of biofilms in pipes can be accomplished by: reducing nutrients; reducing contamination of materials and equipment used for repair and replacement; maintaining proper disinfectant residuals and corrosion control techniques; and preventing cross-connections and backflow problems.
  • • Flush the water delivery system on a periodic basis to keep the lines clean and the pressure of the water constant.
  • • Properly maintain all water storage systems and standpipes to prevent microbial growth and biofilms.
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