Backflow, Cross Connection & Thermal Expansion

Water is essential for life! We all know this for a fact, but we also depend on it to make our lives more comfortable, especially during the warmer months of the year when our usage increases. During the summer we are busy with many outdoor chores involving water such as filling a swimming pool, giving the family pet a bath, washing our cars, cleaning house siding and decks and watering or treating lawns and plants. But regardless the activity or time of year, it is important to keep in mind that it is everyone’s responsibility to protect our safe drinking water supply throughout the year.

Drinking Water Quality

Numerous tests are performed on Clarksville’s water by the expert staff at the water treatment plant to provide citizens with the safest and highest quality drinking water possible. We are proud to report that our drinking water meets and exceeds all federal and state drinking water standards set by the Environmental Protection Agency (EPA). The department goes even further to ensure the safety of our drinking water supply with our ongoing backflow and cross-connection prevention program. This program is mandated through federal and state regulations and City code.

Preventing Threats to Drinking Water

Both backflows and cross connections can pose serious threats to our drinking water supply. This page will explain why and how we can work together, as a responsible community, to prevent these threats. First it is important to know how a backflow or cross connection can occur and how they can result in contaminated water.

Winterize Backflow Preventers

Please remember to winterize your backflow preventer to protect it from freezing temperatures. A damaged backflow preventer cannot do its important job of preventing water from traveling backwards into your water system or even possibly allowing contaminated water to enter the City’s safe drinking water supply. Costly repairs and inspection fees for damaged backflow devices are the owner’s financial responsibility.

Backflow preventers are required on all water meters at commercial businesses, some home businesses and all residential irrigation systems. Call the cross-connection office at 931-553-2489 for help locating your device.

Cross Connection Control Program

The Clarksville Cross Connection Control Program (CCCP) protects our community’s drinking water supply by preventing backflow contamination. Backflow can occur when a change in pressure in the water system causes water in the pipes to flow in the reverse direction. This change in pressure has the potential to pull contaminants into the drinking water distribution system.

As required by Tennessee Code Annotated 68-221-701, the City of Clarksville CCCP ensures that all cross connections have a backflow prevention device installed. Properly installed backflow prevention devices will prevent contaminated water from entering our drinking water system. The CCCP is vital in allowing the City of Clarksville to continue to provide clean, drinkable water to our customers while still maintaining an adequate water supply for domestic and fire protection needs.

What is a "Cross-Connection"?

A cross connection is an actual or potential physical connection between the public water system and any source that could contaminate the public water supply.

Actual: open valve between potable and non-potable

Potential: closed valve between potable and non-potable

Where are Cross Connections Found?

Whenever a plumbing fixture is connected to the drinking water supply, a potential cross connection exists. Most of the time these cross connections are controlled by the use of a backflow prevention device. These devices are usually installed by a plumber when the building is constructed and many of them need to be tested and maintained on a regular basis (generally annually).

What is Backflow?

It's just what it sounds like; the water is flowing in the opposite direction from its normal flow. With the direction of flow reversed due to a change in pressures, backflow can allow contaminants to enter your drinking water system through cross connections.

What Causes Water to Flow Backwards?

Backsiphonage

Backsiphonage is the reversal of normal flow in a system caused by a vacuum or partial vacuum within the water supply piping.

Backpressure

Backpressure is the reversal of normal flow in a system due to pressure higher than the supply pressure.

Your participation in the Cross Connection Control Plan is critical in helping CGW protect the public water system from cross contamination and ensure safe drinking water for all its customers.

WINTERIZING BACKFLOW PREVENTERS

How Do I Winterize My Sprinkler System-RP?

https://www.youtube.com/watch?v=7EDlwoMhHig&t=3s

TN Department of Environment & Conservation

https://www.tn.gov/environment/program-areas/wr-water-resources/fleming-training-center/ftc-redirect/cross-connection.html

American Backflow Prevention Association (ABPA)

https://www.youtube.com/watch?v=tVRtfTIqCl0

https://www.abpa.org

University of Southern California Foundation for Cross-Connection Control and Hydraulic Research (USC FCCCHR)

https://fccchr.usc.edu/

Environmental Protection Agency (EPA) Cross-Connection Control Manual https://www.epa.gov/sites/default/files/2015-09/documents/epa816r03002_0.pdf

What you as a customer of Clarksville Gas & Water need to know about Thermal Expansion

Thermal expansion is among the more serious of plumbing concerns and one that many homeowners know little about. When subjected to pressure under normal conditions, water does not compress. When heated, water expands in volume. For example, the contents of a 40 gallon water tank can expand by half a gallon or more when heated!

A closed plumbing system is one in which potable water has no way to exit a home's plumbing as opposed to an open plumbing system where water inside your plumbing can be forced back into the city water system through the supply line due to issues such as thermal expansion.

The City of Clarksville Plumbing Code requires all new homes and businesses to have a water meter yoke with a check valve installed to protect the water system from backflow. Many older meter yokes do not have a check valve. When Clarksville Gas and Water Department crews are performing any work at a location without a meter yoke with a check valve, the meter yoke and assembly will be replaced.

Required installation of check valves, pressure reducing valves (PRV) and/or backflow prevention devices on your potable water plumbing will create a closed plumbing system. Thermal expansion may cause serious problems in your closed potable water plumbing system.

Thermal expansion is the dangerous increase in pressure due to water being heated in a closed plumbing system. Thermal expansion can cause damage to plumbing fixtures including hot water heaters. The pressure added to a closed system by thermal expansion can wear out seals, damage solenoid valves (like those found on washing machines, dishwashers) and even rupture pipe. The life of water heaters can be greatly reduced with the added stress of thermal expansion. In extreme cases, increased pressure in a gas water heater can cause the flue inside to collapse, creating a carbon monoxide leak and even at times causing water heater explosions.

Measures you should take to control thermal expansion in your closed plumbing system

Indicators of Thermal Expansion:

The relief valve on the hot water heaters drips.
Hot water pipes creak and make noise during water heater recovery.
Damage and premature failure of plumbing fixtures, especially hot water tanks. Water heaters may not last very long or they may begin to leak.
Hot water is present in the cold water lines.

Dangers of Thermal Expansion:

Most manufacturer’s warranties do not cover uncontrolled thermal expansion damages.
Pressure increases can cause deterioration and dangerous malfunction of the water heating equipment.

Devices that will help or eliminate the negative impacts of thermal expansion.

Clarksville Plumbing Codes require that a thermal expansion device be installed when there is a closed plumbing system. A device primarily used for thermal expansion is a thermal expansion tank that connects to the water heater or service line, which will accommodate volume increases if properly maintained. Other options include relief valves with discharge outlets that simply drain whatever the system cannot hold, and special toilet fill valves that drain excess volume into the toilet tank.

Thermal Expansion Tanks

Thermal expansion tanks feature a rubber bladder/diaphragm that separates an air chamber from the rest of the tank. Air is pumped into the air side of the expansion tank to match the pressure of the water supply. When water expands, instead of building pressure in the confines of the water heater or plumbing, it enters the expansion tank, compressing the air. Once expansion has stopped, the compressed air pushes the water back into the plumbing system.

It is important to know that the water heater temperature and pressure relief valve should not be used as a means of controlling thermal expansion. Instead, contact a plumbing professional if you suspect a problem. The plumber can schedule an inspection and install proper thermal expansion control methods. Contact the Water Distribution Department at (931) 553-2497 for more information.

More helpful information is available at the website links provided here for brief videos explaining the relief valve on the water heater and the installation of an expansion tank.

Relief Valve Keeps Opening? Thermal Expansion Explained | Repair and Replace YouTube Video

What Is This Tank? How to Replace and Maintain a Water Heater Thermal Expansion Tank YouTube Video