Back Flow Prevention
A guide for residents, contractors and business operators
As part of its obligation to supply safe drinking water the City of Horseshoe Bay maintains a program to prevent back flow and cross connections between potentially hazardous substances and the City water supply.
Back flow is the unwanted reversal of flow of water which might carry unclean water or other, hazardous substances into the public water supply and private plumbing. Back flow can occur in a number of circumstances that might draw water from places such as garden fountains, swimming pools, or lawn sprinkler systems into City water supply lines. Back flow can also carry water into your plumbing if it is connected to any outside water source. One example would be a garden hose connected to an external faucet with the end left in a mud puddle in a garden area.
Information on this page covers the following:
- Back flow causes
- Preventing back flow
- Determining what type of back flow preventer to use
- Finding a back flow tester
- Other back flow needs
- Temporary Construction connections
- Switch-over valves between Lake LBJ and the City water system prohibited
Back flow causes
Two conditions cause back flow: back siphoning and back pressure. Back siphoning can occur if pressure in a pipe system drops and causes a vacuum that pulls water from other areas of the system toward the vacuum.
Heavy usage elsewhere or a main break could cause water pressure to drop in main lines, causing back siphoning to occur which would pull water from your plumbing or irrigation system into the public supply and your home’s plumbing.
Back pressure generally occurs when a pump is introduced to apply pressure to a system of pipes, or water comes under the influence of gravity, such as raising the height of the water above the ground. Simply lifting the end of a hose filled with water would place the contents of the hose under back pressure.
Preventing back flow
The City requires back flow prevention devices to be installed anywhere there exists a connection that could allow tainted water into the City system or private plumbing. These devices are subject to testing by a qualified back flow prevention assembly tester upon installation. In many cases they are subject to periodic tests later, as well.
Common locations where back flow presenters are required are swimming pool automatic refill lines, refill lines for garden ponds and decorative fountains, and landscape irrigation systems. We also require hose bibb vacuum breakers on all external faucets to prevent back flow from garden hoses.
Back flow devices must be considered “approved,” which means they meet requirements of recognized plumbing standards organizations.
Plumbing Codes and State law dictate minimum standards for back flow prevention. Public water systems such as the City Utilities Department must meet or exceed the state standards and carry the responsibility for enforcing them.
Determining which type of back flow prevention device to use
The type of back flow preventer applied in a situation depends on the level of hazard and the type of backflow which could occur.
The Texas Commission on Environmental Quality classifies water as either health hazard or non-health hazard. Health hazard means the water contains organisms or chemicals that could seriously sicken people or even lead to death if consumed. Non-health means the water is not likely to cause serious illness, but would not be desirable to drink from the standpoint of taste or appearance.
Types of back flow devices and their applications in terms of hazard level
- Reduced pressure zone back flow prevention assembly (RP): health hazard, non-health hazard, protects against back siphoning and back pressure
- Double check valve back flow prevention assembly (DCVA): non-health hazard, protects against back siphoning and back pressure
- Pressure vacuum breaker (PVB): health hazard, non-health hazard, protects against back siphoning, but not back pressure
- Spill resistant vacuum breaker (SVB): health hazard, non-health hazard, protects against back siphoning, but not back pressure
- Atmospheric vacuum breaker (AVB): health hazard, non-health hazard, protects against back siphoning, but not back pressure.
- Air gap: health hazard
Horseshoe Bay residences and businesses may have multiple locations needing back flow preventers. Our most common applications in Horseshoe Bay are listed here. The unit chosen for a given installation must be appropriate for the system design and site conditions, including consideration of whether back siphoning or back pressure is likely to occur. Further, it must be installed in accordance with plumbing codes, manufacturer specifications, and engineering guidelines for the type of unit to be used.
Irrigation systems: All landscape irrigation systems must have a back flow preventer. Any testable back flow preventer may be used unless the system injects pesticides or fertilizer. If the system injects chemicals it must have a reduced pressure zone back flow preventer (RP).
Double Check Valve assemblies are the most common type used on irrigation systems in Horseshoe Bay.
Horseshoe Bay rules require that irrigation systems which do not inject chemicals must have their back flow preventer tested upon installation and then every 5 years afterward.
In the case of chemical injection into the irrigation system, the RP must be tested upon installation and then annually.
Swimming pools: Automatic refill lines on a residential swimming pool must have either a PVB, an RP or an Air Gap. These units on swimming pool applications are subject to testing upon installation. The City does not require further testing, but recommends periodic testing for units on residential swimming pools.
Unlike residential pools, public or community pools must use only RP devices or Air Gaps on their refill lines. An RP on a public or community pool must be tested upon installation and then annually.
An air gap on a swimming pool refill pipe must be easily accessible for inspection and meet the strict definition of an air gap as defined in plumbing codes and state regulations. Refill lines and the back flow preventer type and location must be indicated on pool construction plans.
Fountains and garden ponds: Automatic refills on these water features must have either a PVB, an AVB or RP back flow preventers. These water features are considered a health hazard if back flows occur from them. Refill lines and the back flow preventer type and location must be indicated on construction plans. Any back flow preventer installed on a fountain or garden pond must be tested upon installation and then annually.
Connecting irrigation to fountains, swimming pools and garden ponds prohibited: State law and City ordinance hold that no irrigation system may be connected to a fountain, swimming pool, or garden pond. These water features may only be filled with potable water. Water which has entered an irrigation system is not potable.
Properties with water wells: Properties on well water must have an RP back flow preventer on their service line isolating the public water system from the property. The RP for a property with a water well must be tested upon installation and then annually.
Non-conforming back flow preventers
Back flow preventers not conforming to these rules for a given applications and which are worn out or broken and require replacement, must be replaced by a back flow preventer which does comply to the rules for the given application.
Finding a back flow tester
Testing to assure function must be done by a back flow tester holding a license issued by the Texas Commission on Environmental Quality, the state’s environmental agency. To find a qualified tester, go to the website Vepollc.com and click on “Back flow Management” and then “Registered BPAT list.” Choose the City of Horseshoe Bay from the drop down list. A list of testers registered to test in Horseshoe Bay will appear.
Other back flow needs
Back flow preventers maybe needed on a number of other locations in a residence or businesses either to isolated the property from the public water supply, or to block internal backflows in a building’s plumbing system. Examples are medical offices, restaurants and convenience stores.
All hose bibbs must have a screw-on type vacuum breaker attached at all times to prevent water siphoning from garden hoses into a structure’s plumbing.
Temporary construction connections
Back flow prevention measures must be maintained on site at all times during construction. Temporary water will be allowed after the contractor installs a hose bibb assembly consisting of a vertical PVC riser at the water meter with a hose bibb on a 90-degree elbow at the top. A vacuum breaker must be attached to the hose bibb at all times. The discharge opening from the vacuum breaker must be at least 12 inches above grade. The riser must be firmly attached to a sturdy rebar or wooden steak to add structural stability to the assembly. Direct connection between the water meter and the structure plumbing before the structure is substantially complete is prohibited unless a double check back flow assembly is installed and immediately tested to assure it is working.
Switch-over valves between Lake LBJ and the City water system prohibited
Residential irrigation systems must be permanently connected to either City potable water or Lake LBJ. They may not have switch valves to change the water source between lake and City water. Such an arrangement puts the customer ‘s plumbing and City potable lines at risk of contamination caused by backpressure from the irrigation pump. Any lake-city supply switch valve existing in the City must be disconnected and pipe ends permanently capped, regardless of its installation date.