Very Basic Question on Testing Potable Water Lines

[TexasCHe]

I have just a very basic question on tests run on potable water lines after repairs have been made. Among other things such as flushing and disinfecting lines you have to perform a hydrostatic test on the lines. This makes sense from an integrity view point because you want to ensure you’re not losing water thus creating other problems. But in addition to that, does a leak represent a potential point of contamination? If so I assume it would have to be during a system pressure loss. Any general comments would be appreciated!
Thanks

 

[bimr]

Potable water distribution systems are tyically required to maintain a normal working pressure of 35 psig. Presumably, this minimum pressure will serve to minimize the potential for contamination from leaks.

 

[btrueblood]

There are times when water mains may experience external pressure higher than internal. Shut-downs for repairs, or during fire situations for regions that actively control water mains during emergencies, are just a couple of situations I can think of.

 

[coloeng]

While flushing is typically required after fixing a leak to remove air and any minor debris from the repaired water line, it is very difficult to disinfect and pressure test the water line. Because you typically have services that are attached to the water line, unless you turn all of the services off, you could get the chlorinated water or high pressure from the pressure test into these services. Additionally, if you take a sample of the water to check for bacteriological activity after fixing the leak you typically have to wait 24 hours for confirmed results.

Anything that will delay returning a water line to service after fixing a leak is problematic from a customer service perspective. Admittedly, you want to ensure that the water does not have contamination. That is one of the reasons for maintaining a disinfection residual. The other thing that needs to take place is ensuring that the repair crew practices good protocol for keeping the area disinfected and disinfecting any parts that are used in the repair.

 

[zabrab]

Pennsylvania DEP just implemented a new policy that might be of use to you:

Policy for Determining When Loss of Positive Pressure Situations in the Distribution System Require One-Hour Reporting to the Department and Issuing Tier 1 Public Notification

It's 9 pages and the bulk of it deals with what they consider best management practices for main breaks that result in loss of positive pressure.

http://www.elibrary.dep.state.pa.us/dsweb/Get/Document-76813/383-2129-004.pdf

 

[TexasCHe]

Thanks all!