Backflow Prevention Programs - A Wholistic Approach

Protection of the water reticulation system requires a wholistic management approach. Backflow prevention and cross connection control is one part of that wholistic approach.

Here we look at one project, and the “closed” system objective, and some features of a good backflow prevention program.

A major steel manufacturer on the Mornington Peninsula recently completed reconstruction of its water meter stations. The project took three years of planning, design and construction to ensure no loss of production, and seamless shut down.

South East Water requested installation of backflow devices at five water meter stations as part of its’ containment backflow prevention program. The water had not been shut down for 20 years. The steel piping was deteriorating, and this presented a perfect opportunity to exchange the water meters and replace the old valves and piping.

From a plumbing perspective, the project was interesting because there are few above ground ductile iron water meter assemblies of 200 to 375 mm in size for fire and general water. The piping was replaced with flanged piping spools constructed of cement lined ductile iron to provide a heavy duty, impact resistant solution capable of withstanding high thrust and pressure.

One of the critical issues was to keep pressure losses to a minimum. This was achieved by removing the old meter valves, check valves and above ground steel piping. The internal diameter of old steel piping had reduced significantly due to the build up of rust and scale.

Reduced Pressure Zone backflow prevention devices were installed. This type of device can reduce the pressure by as much as 100 kPa. It was important to select backflow valves with low head loss characteristics, and after comparing a number of products; the Wilkins Model 375 was selected. The valve head loss is around 65 kPa at 75 litres/second.

At the same time, there was an increase in supply pressure. An open reservoir was decommissioned and supply was then from an adjacent reservoir of higher elevation and this resulted in a pressure increase of 50 to 60 kPa. And so with the combination of increase in supply pressure and careful valve selection, the static pressure loss to the site was negligible. If anything, water flows were improved.

The water industry and South East Water in particular have led the way in backflow prevention and recognized that backflow prevention plays an important role in protecting the potable water supply. Containment backflow prevention at the outlet of water meters is one small but important part of the South East Water HACCP system. This system “Hazard Analysis and Critical Control Point” is a standard developed for the food industry but adopted by South East Water for the supply of potable water.

Cross connection control and water mains of the future

Most water utilities in Australia have developed and implemented backflow prevention policies to reduce the likelihood of cross connections and backflow to the mains water supply. However, “a lot more water will pass under the bridge” before there is full and uniform acceptance and understanding of backflow prevention.

Some water utilities have only implemented backflow prevention policy for medium to high-risk industrial and commercial properties. There are other risks such as:-

1. Fire services that are unmetered and unmonitored, and have defective check valves.
2. Private water main extensions.
3. Low-level fireplugs.
4. Hydrants and hydrant standpipes.
5. Filling stations and water cart vehicles

In addition, the national drive for greater water efficiency through offering incentives, tightening regulations and increasing cost is creating more non-potable water sources and potential cross connections with rainwater tanks, greywater and greywater systems and recycled water schemes.

Water utilities with backflow prevention policies that address all actual and potential cross-connections in concert with a retrofit plan are moving to a “closed” water reticulation system. This is a system where there is a reduced likelihood and entry points for potential contaminants and pathogens; and all connections are “controlled”.

A good backflow prevention program

The relevant Australian Standards are:

AS/NZS 3500.1 Part 1, Water Services, This is an installation standard for plumbers

AS.2845.1, 2 and 3, Water supply – Backflow prevention devices, These are standards for materials, design and performance requirements of backflow devices, Air gaps and break tanks, and Field testing and maintenance

Generally, registered or licensed plumbers are required to complete a course in backflow prevention to become accredited to test and maintain backflow devices.

Water utilities can apply the above standards and plumbing qualification in implementing the backflow prevention program, however there are issues to be considered in the structure of a good program and information to the customer.

1. The customer must understand that the water will need to be shut down annually to clean the line strainer and test the backflow device. There have been problems with properties having critical water supplies but only one backflow device. Eg- manufacturing operations using water for product or cooling; pressure operated valves. The customer may need two backflow devices installed in parallel to ensure no disruption to their internal processes and equipment.
2. A plumber without the testing accreditation can install the device, but only an accredited plumber can inspect and test the installation. AS/NZS 3500.1 states that, “Testable backflow prevention devices shall be commissioned and tested after installation and prior to service”. The customer should be informed that the device should be tested after installation, before the water supply is turned on.
3. The device is required to be commissioned and tested by an accredited plumber, and thereafter tested annually. There may be some reluctance to fail the first test if the customer might choose to engage another plumber that will pass the first and subsequent tests. A solution is to audit some passed test reports and all failed test reports.
4. The purposes of water use and connections at properties are constantly changing. Random audit surveys of low to medium risk property connections may reveal elevated risk and the need to install high hazard containment backflow prevention.

A good backflow prevention program identifies all actual and potential cross-connections, has set policy for new connections and a timetable for assessment and retrofit of existing connections. Also important, are a competitive market for installation and testing, and an audit system for verification of compliance.

Peter Wenning is director of Wenning Technical Services. As a Plumbing Inspector with Melbourne Water 15 years ago, he attended several incidents of backflow and contamination of the potable water supply. He later gained experience in water meter management. Now a Hydraulic Services Consultant he has experience in designing backflow prevention for industrial and commercial properties, cross connection surveys, and implementation of backflow prevention programs at South East Water and Yarra Valley Water.
Email Peter at pwenning@bigpond.com

Thanks to Plumbing Connection Magazine for their kind permission to reproduce the above article