Last month, we discussed how certain substances used in disinfection could damage piping systems, as well as guidance from the International Plumbing Code (IPC) and Uniform Plumbing Code (UPC).

This month’s column will go over disinfection “methods” noted by the codes.

Currently, there is no consensus industry standard directed toward flushing and disinfection of premise plumbing/building water systems, either before occupancy of the building or in response to a bacteriological problem or closed, stagnant plumbing system. The method provided in the IPC and the UPC with respect to disinfection before usage/occupancy are vague in practical guidance and are not really methods at all. 

In other words, these code sections tell you “what” to do, i.e., fill the piping system with either of two chlorine-water solutions and hold it in the piping for a stated period, but the details on “how” this is to be accomplished are lacking. Also, the codes call for a minimum level of chemical concentration in parts per million (ppm) but no maximum levels.

The American Water Works Association (AWWA) Standards C651 and C652 — for disinfection of utility water mains and water-storage facilities, which are referenced in the IPC — are neither translatable nor easily adaptable for implementation in building plumbing systems, which have smaller pipe sizes. AWWA C651 was developed to flush and disinfect utility water mains with pipe sizes 4 inches and larger, not for flushing and disinfection of building water systems. 

The foreword (which is for information only and not a part of AWWA C651), as well as the scope and purpose of the standard, informs that the standard is intended for water mains, which utility water mains (and water storage facilities) are materially and significantly different from premise plumbing systems in both construction materials, size and operation. 

No one reading either AWWA C651 or AWWA C652 would be able to competently employ the direction stated therein to a premise/building plumbing system. For example, AWWA C651 gives four methods of disinfection, only one of which (continuous feed) has any plausibility of being applied to a premise/building plumbing system. 

Further, in the tables used to determine chlorine dosage and flushing velocity, the smallest pipe size accounted for in AWWA C651 is a 4-inch pipe (Tables 1 through 4); however, most buildings have piping smaller than 4 inches. Only in the most basic of terms can anything resembling an overall method that can be applied to premise plumbing systems be gleaned from reading AWWA C651. 

The method would, in essence, simply be a broad statement of the order of performance, which, in my reading of AWWA C651, consists of the following: 

1. Flush the system with water until the water runs clear, removing obvious dirt and debris;

2. Fill the system with a water-chlorine solution;

3. Valve off the system and wait a specified time, depending on the chlorine concentration of the solution used;

4. Sample/measure the residual;

5. Safely flush the hyper-chlorinated water out of the system;

6. Verify by bacteriological testing.

These steps mentioned in AWWA C651 are more numerous than the steps set forth in the referenced sections of the IPC and UPC. Those code sections do not require the sampling and measuring of a water treatment chemical residual to be performed during or after the waiting period or that the hyper-chlorinated water should be safely discharged.

Controlled Flushing and Disinfection

ASHRAE Guideline 12, Minimizing the Risk of Legionellosis Associated with Building Water Systems, provides guidance on flushing a hot water system with very hot water in a high-temperature “heat and flush” decontamination effort. I have found that most water heaters are not designed to perform thermal disinfection at the temperature rise and flow rates required to quickly disinfect a system. 

Plus, thermal disinfection only addresses the hot water system. Note that a more detailed flushing procedure is currently being developed as an appendix to Guideline 12 (GL12). However, GL12 provides little guidance on hyper-chlorination procedures for decontamination.

The piping manufacturer, plumbing design engineer and the water treatment provider need to work together to develop a controlled flushing and disinfection procedure that limits excessive chemical exposure and contact time with the piping system. The steps I would suggest are more numerous than either the code or AWWA C651 and would include but not be limited to the following:

1. Determine all pipe, fitting, valve and equipment manufacturers and materials of construction. 

2. Obtain manufacturers’ chemical resistance data to establish the maximum ppm levels allowable and the required contact time for the water treatment chemical to be used to minimize oxidation/damage to the system. 

3. Document the materials, the chemicals to be used, the concentration in ppm, the contact time and who is performing the work. Document the date, time and data from the entire flushing and disinfection process and keep records to show that such processes were performed.

4. Locate chemical injection points and flushing locations. 

5. Identify testing methods for ppm of water treatment chemical to be used (test strips or chlorine meters).

6. Establish maximum and minimum ppm levels and contact time required for effective disinfection. 

7. Pre-mix disinfection chemicals in tanks or establish a flow-proportioning pump that can be accurately controlled with a chlorine meter.

8. Establish a procedure for flushing water at every fixture, a required number of simultaneous fixtures to be flushed and a schedule of flushing times.

9. Turn off the hot water system and flush out hot water that can affect the chemical oxidation rate.

10. Flush the cold and hot water systems with water at approximately 3 feet/second velocity until the water runs clear at every fixture. This removes dirt, sediment and debris.

11. Determine the chlorine residual and perform bacteriological testing at the source water to establish a baseline.

12. Fill the system with a water-chlorine solution; flow water from every fixture until water treatment chemical residuals of a sufficient amount are present.

13. Valve off the system and wait a specified time, depending on the chlorine concentration of the solution used.

14. Measure the water treatment chemical residual at remote fixtures at the beginning, at regular intervals and at the end of the contact time period.

15. Safely flush all the hyper-chlorinated water out of the system to prevent oxidation and corrosion damage.

16. Verify effectiveness by testing for chlorine residuals and performing bacteriological testing.

17. Repeat steps if bacteriological testing shows system is still contaminated.

18. If source water is contaminated, notify the water purveyor to flush water mains and check their water treatment chemical residuals. 

Good Intentions, Bad Results

When investigating Legionella outbreaks or new piping systems springing leaks, I see many installations where the piping system has been destroyed by the disinfection process. Without proper training, the disinfection of a piping system can destroy the piping and expose the building occupants to toxic levels of water treatment chemicals. 

I have seen building owners and contractors “combine” the flushing guidance in GL12 with the chlorine ppm solutions mentioned in the code to quickly disinfect their building water piping systems by flushing through (and not holding) a water-chlorine solution in the piping system. Sometimes, systems are filled with chlorine solutions in the thousands of ppm because there was not a good way to proportion the chemicals accurately. I have also seen high levels of chemicals left in the system. 

In most cases, these activities are performed after a reported case of Legionellosis from a tenant. When a building is already in use, the process of hyper-chlorination can be very disruptive to building occupants because water must not be used during the process of hyper-chlorination; temporary evacuations are sometimes the case, or shutting down the water system and distributing bottled water. 

This demonstrates the need for an industry standard for emergency flushing and disinfection procedures for building water systems/premise plumbing systems that will consider the piping system materials, water treatment chemicals and required contact time at various concentrations with respect to corrosion/oxidation damage to the pipes, and toxicity to humans.