Cross Connection Control - Frequently Asked Questions
WHAT IS BACKFLOW?
Backflow is defined as the undesirable reversal of flow of water or other substances into the potable water distribution system. Backflow prevention is a federally mandated program that requires the installation of backflow prevention assemblies. These assemblies prevent water, once delivered to the customer, from flowing back into the distribution system. Public health must be maintained by preventing the contamination or pollution of the municipal water supply system. Residences, food processing plants, medical and dental facilities, industrial plants, and all other water customers must have clean, safe water.
WHAT CAUSES BACKFLOW TO OCCUR?
Backflow may occur when there is an imbalance in the hydraulic forces in a water distribution system where unsafe water can be forced or drain into the drinking water system.
Two conditions create backflow: 1) back pressure, and 2) back siphonage.
Back Pressure occurs when pressure in the down stream piping is higher than the supply pressure, thus "pushing" the water (or other substance) back into the drinking water supply.
Back Siphonage occurs when pressure at some point in the water distribution system drops below atmospheric pressure. This decrease in water pressure enables water (or other substance) to "siphon" back into the drinking water supply.
WHAT IS CROSS CONNECTION?
An arrangement of piping that allows the public drinking water supply line to be connected directly to an actual or potential source of contamination. Some examples could be the ordinary garden hose attached to a service sink with the end of the hose submerged in a tub full of detergent, water supply lines connected to bottom-fed tanks, water supply lines to boilers, cooling towers, landscape irrigation systems, etc.
WHAT IS A BACKFLOW PREVENTION ASSEMBLY?
A backflow prevention assembly prevents a reverse flow of liquid or gases from occurring. The selection of the proper backflow prevention assembly for installation at any one particular location is important in relation to the kind of toxic or nontoxic fluid that could backflow, and whether the potential for back pressure or back siphonage exists.
Listed below are the six basic methods used to prevent backflow:
1. Air Gap.
2. Reduced Pressure Backflow Assembly.
3. Double Check Valve.
4. Pressure Vacuum Breaker.
5. Atmospheric Vacuum Breaker
6. Spill Resistant Vacuum Breaker
WHERE DO I GET ONE, AND HOW MUCH DO THEY COST?
Usually, at plumbing supply outlets, landscape irrigation supply outlets, and some home improvement stores. The cost varies upon the size, type of assembly, and the installation location.
WHERE SHOULD THE ASSEMBLY BE INSTALLED?
The assembly should be installed on the customer side of the water meter, on private property as close to the water meter as possible. Exceptions may be allowed in some instances if approved by the City of Glendale, Cross Connection Control Specialist, prior to installation.
MAY THE ASSEMBLY BE PLACED UNDERGROUND IN A VALVE BOX OR VAULT?
No. However, you may landscape around it or construct a fence or a wall around the assembly provided adequate clearance is available for the testing and maintenance.
WHO INSTALLS THE ASSEMBLY AND WHAT IS THE PROCEDURE?
The water customer is responsible for installing and maintaining backflow prevention assemblies. (Please refer to the "City of Glendale Customer Checklist for Backflow Prevention Assembly Installations" for procedural requirements.) The installation is to be performed by a contractor licensed by the register of Contractors Office.
IF THERE ARE SEVERAL WATER METERS LOCATED AT ONE FACILITY, HOW MANY ASSEMBLIES ARE REQUIRED?
One assembly for each water meter is required. This is usually less costly and will provide water to the customer through one connection if another assembly is shut off for testing or repairs.
DOES THE INSTALLATION AFFECT THE WATER PRESSURE TO THE BUILDING?
Yes. All assemblies use up water pressure as water flows through the device. The amount varies depending upon the type and size of assembly - usually it ranges from 6 to 12 PSI (Pounds Per Square Inch).
ONCE INSTALLED, WHAT KIND OF MAINTENANCE IS REQUIRED?
The assembly must be maintained in acceptable working order at all times. In addition, the water customer is responsible for annual testing and associated costs.
HOW OFTEN SHOULD THE ASSEMBLY BE TESTED FOR COMPLIANCE?
At the time of installation, relocation, repair, and annually thereafter. The Arizona Department of Environmental Quality requires annual testing of backflow assemblies. The City will mail you a notice annually informing you of the test.
IF A CUSTOMER HAS A PRIVATE WELL BUT USES IT ONLY AS A STANDBY, WHY IS THE INSTALLATION OF AN ASSEMBLY REQUIRED?
The City of Glendale does not have any control over the quality of water supplied by a private well and therefore, by State regulations, may not permit the water to backflow into its system.
IF A NEIGHBOR DOES NOT NEED TO INSTALL ONE OF THESE ASSEMBLIES, WHY DO I?
Each water service is evaluated for actual or potential cross connections and/or the
degree of hazard should backflow occur.
WHY DO I HAVE TO INSTALL AN ASSEMBLY NOW, WHEN I'VE BEEN HERE FOR YEARS WITHOUT NEEDING ONE?
New Federal and State mandates require commercial, industrial, and residential water customers to install and maintain backflow prevention assemblies. The City of Glendale will specify where and how customers must comply with these mandates and requires these assemblies be inspected and tested periodically.
The reason for this requirement is simple -- the customer expects to receive a clean, constant supply of water. Should a customer's own private water system become contaminated, the City of Glendale must protect its water from any contaminants that may find their way back through the pipes. The extra cost and inconvenience involved in installing and maintaining these assemblies is necessary to ensure clean drinkable water to all customers.
WHAT IS THE DIFFERENCE BETWEEN A TOXIC AND A NONTOXIC SUBSTANCE?
A toxic substance is any liquid, solid, or gas which creates a danger to the health and well being of the consumer. For example, chemicals, solvents, and poisonous substances are toxic. A nontoxic substance is one that may create a nuisance if consumed or is aesthetically unpleasant. For example, soap, food, and soda pop are nontoxic, but undesirable in the water supply.