Commissioning and Disinfecting Copper Plumbing Systems

Once a copper plumbing system has been installed, the system should be flushed and commissioned for service.

While there are no special requirements for commissioning and disinfecting a copper system, there are precautions that should be taken to ensure the commissioning and disinfection procedures do not damage the system.

As with the installation or repair of any piping system, of any material, it is important to flush the system of any potential contaminants prior to putting the piping into service. Installation procedures should ensure that avoidable contamination to the interior of the system is minimized. Flushing or commissioning procedures, should account for contaminants that could be expected due to system installation, as well as environmental contamination (microbial contamination).

As with any material, a clean installation starts with keeping dirt and debris out of the tube and fittings prior to installation. Tube, fittings and components should be inspected upon deliver to ensure that the interior surfaces are clean and free of dirt and debris, and should be stored in such a way until use to prevent contamination of the interior surfaces.

For copper systems, installation procedures should ensure that metal chips from cutting, reaming and cleaning the copper tube do not enter or remain within the system following joining. A simple method to ensure that copper chips or dust do not enter or remain in the system is to tie a string around a clean rag and push the rag into the piping prior to cutting, reaming, cleaning and joint fit up. Once these processes are complete and the joint is ready to be made, a simple tug on the string will remove the rag and pull all dust and debris from the joint preparation out of the system interior. In making soldered joints, fluxes meeting the requirements of ASTM B813 should be used so that the residue after completing the joint can be easily removed with a water flush.

For water systems, potable or otherwise, before putting the system into service the system should be flushed with water at a velocity of at least 3 feet per second. This will remove any copper chips or dust that remained in the system during installation, and will also remove any flux residues from the soldering operation, if the flux used was a B813 flux. If a petrolatum flux that does not meet this standard was used, it is unlikely that a water flush at any reasonable velocity will remove the residue.

For potable water piping systems, many municipalities, water utilities, property owners/managers, and inspection agencies have required that systems be disinfected prior to use by employing chlorination procedures outlined in ANSI/AWWA Standard C651. This standard was originally developed for the disinfection of large diameter water mains, and in many cases has been inappropriately adapted by agencies and code bodies for application to water services/laterals and water distribution piping within buildings. In general, this procedure requires that bleach or chlorine tablets be introduced into the water system to produce a chlorine content of either 50 ppm (parts per million) or 200 ppm measured as Cl2.  This solution is then allowed to stand stagnant in the piping system for 24 hours (at the 50 ppm chlorine level) or 3 hours (at the 200 ppm chlorine level).  Following this the appropriate stagnation time, the system is bacteriologically tested to confirm the absence of bacterial contamination, or tested for chlorine residual to confirm no more than a percentage loss of chlorine content as a surrogate to indicate that disinfection was successful.

The error in applying this disinfection method to copper systems lies not in the shock chlorination, but in using the measurement of residual chlorine levels after stagnation as the signal for disinfection success. Chlorine is a strong oxidizing agent that reacts readily with materials in the piping system, including copper, other metals and plastics to created oxide and chloride compounds. In the case of new copper systems, chlorine reacts with the copper and water to create copper oxides and chlorides, thus depleting the chlorine residual even in the absence of bacterial contamination. In applying shock chlorination to a copper system, a reduction in the chlorine residual over time will nearly always occur, and does not indicate that the chlorine is being depleted in fighting bacterial contamination. Therefore it is inappropriate and often damaging to the copper system to shock chlorinate the system, measure the chlorine residual and then repeat the shock chlorination and measurement multiple times trying to achieve a specified minimum drop in the chlorine content.  Multiple, repeated shock chlorination sets up unstable corrosion films on the interior of the piping system surfaces that can lead to rapid or long-term failure depending on the chemistry of the system’s water.  This is not a failure of the piping material, or a failure of the shock chlorination to disinfect the system, it is a failure of the application of the acceptance criteria for the shock chlorination.

For copper potable water systems, where disinfection is required prior to putting the system in service the system can be filled with potable water that is chlorinated to either 50 ppm or 200 ppm as the ANSI/AWWA C651 Standard suggests, and then held stagnant for 24 hours or 3 hours respectively. Following stagnation, the system should be flushed with clean, potable water and put into service (see the paragraph below). If confirmation of disinfection is required, bacteriological testing should be performed. Chlorine residual should not be used for acceptance/proof of disinfection. Should bacteriological testing indicate contamination, shock chlorination can be repeated – however shock chlorination should not be conducted more than twice.

If, following shock chlorination, the system is anticipated to be held stagnant prior to building completion or occupancy, the system should be flushed with clean, potable water so that all excess chlorine in excess of the residual content of the delivered water is removed. If only a portion of the system is to be installed, disinfected and tested (for example water services/laterals installed at the time of water main installation in anticipation of future building construction), either flush and fill that portion of the system with potable water as above and seal/cap the stagnant end of the system, or preferably purge that portion of the system of all water/moisture and then seal/cap that portion of the system to prevent contamination or the ingress of corrosive substances/water.

For more information on the flushing/commissioning copper systems and the negative impacts of improper flushing or improper use of chlorine residual as a measure of disinfection success, see Lead and Copper Corrosion Control in New Construction (Report #4164, Water Research Foundation, 2011) which is available for purchase.