Protecting Your Sprinkler Backflow From a Georgetown Freeze

The part of a Georgetown sprinkler system most likely to break in a hard freeze is the backflow preventer, the brass assembly that sticks up out of the ground near the water meter. It holds water above grade with nothing around it, so it freezes first, and the fix is to shut the water off to it and drain it before the temperature drops, not after.

The rest of the system mostly sits underground and rides out a short Central Texas freeze. Here is why the backflow is different, what to do the evening before a freeze, and what Texas rules require if it cracks anyway.

Why does a freeze crack a sprinkler backflow preventer?

Water grows as it turns to ice, and a sealed brass body has nowhere to put the extra volume. Colorado State University Extension explains that water contracts as it cools until it reaches 39 degrees Fahrenheit, then expands as it freezes at 32 degrees. The same publication says water "increases in volume by one-eleventh, so 11 cubic feet of water will form approximately 12 cubic feet of ice," enough force to burst pipes and crack valves.

The City of Georgetown gives homeowners the same warning about household plumbing: in severe cold, water in pipes can freeze, expand and burst the pipe. A backflow preventer is that problem in its most exposed form.

Why is the backflow above ground in the first place?

Texas rules put it there on purpose. The Texas Commission on Environmental Quality's landscape irrigation rule, 30 TAC § 344.50, requires a pressure vacuum breaker to sit at least 12 inches above the highest downstream sprinkler or pipe, and a reduced pressure assembly to sit at least 12 inches above ground so it can never be submerged.

That height is what keeps lawn water from siphoning back into the drinking water supply. It is also what leaves the assembly standing in the wind on the coldest night of the year, which is why it should be protected rather than buried.

Does Georgetown really get cold enough to matter?

Georgetown gets cold enough often enough that every system should be ready by November. The 2023 USDA Plant Hardiness Zone Map puts ZIP codes 78626 and 78628 in zone 9a, an average coldest night of 20 to 25 °F, and ZIP 78633 in zone 8b, 15 to 20 °F.

The extreme case is recent. The National Weather Service Austin/San Antonio summary of the February 2021 winter storm records 5.2 inches of snow in Georgetown, 3 to 8 inches along much of Interstate 35, temperatures that fell into the single digits and teens, and burst water pipes across the state.

What should you do the evening before a hard freeze?

Shut off the water to the irrigation system, drain the backflow, and insulate it. In that order:

• Close the irrigation isolation valve. TCEQ rule 30 TAC § 344.62 requires every new system to have an isolation valve between the water meter and the backflow assembly. That valve, not the house shutoff, is the one that stops water to the sprinklers.
• Know where the main shutoff is too. The City of Georgetown says a slab home's main shutoff is usually in the yard, about 2-3 feet from the meter box toward the house, and asks owners to turn valves by hand only.
• Drain the assembly. Colorado State University Extension recommends leaving the ball valves and test cocks half-open over a freeze, because valves left fully open or fully closed trap water that expands and splits the body.
• Wrap it. An insulated cover or a towel and a bucket over the drained assembly buys extra degrees on a night that only dips briefly below freezing.
• Turn the controller off. A system that runs its morning schedule into a freeze sprays ice onto sidewalks and plants.

Never blow out a backflow assembly with an air compressor. Colorado State University Extension warns that pressure vacuum breakers and reduced pressure assemblies "must never be blown out with compressed air" because the heat can melt the rubber seals inside.

How do you turn the system back on after the freeze?

Close the test cocks and ball valves first, then open the supply slowly. Colorado State University Extension says opening the ball valves slowly prevents water hammer damage to the rest of the system.

Then run each zone and look. Water spraying from the assembly body, a hiss at the valve box, or a zone that will not hold pressure means something split. Georgetown Water's current Stage 1 schedule bans irrigation between 9 a.m. and 7 p.m. and all day Monday, so test a zone briefly by hand rather than programming a midday run.

What happens if the backflow cracks anyway?

A cracked backflow preventer has to be repaired or replaced, and Texas then requires a test before it goes back in service. Under 30 TAC § 344.50(e), every backflow assembly must be tested by a licensed backflow prevention assembly tester upon installation, repair, replacement or relocation, and § 344.52 gives the irrigator ten business days to send the result to the local water utility.

B&B Landscaping & Masonry repairs and re-tests freeze-damaged backflow preventers as part of its irrigation repair work in Williamson County, led by a Texas Licensed Irrigator (LI0028648). The same visit is a good time to fix the leaks and broken heads a freeze tends to expose.

Is a freeze sensor worth adding?

A freeze sensor is the easiest insurance against a controller running on a cold morning. The City of Georgetown's sprinkler maintenance guide notes that a rain and freeze sensor automatically shuts off an irrigation system during rain or freezing temperatures, and TCEQ rule § 344.62 already requires a rain or moisture sensor whenever an existing controller is replaced.

Beds that do not need spray heads at all are another way out of the problem. Converting them to drip or to a xeriscape design shrinks the system and the number of parts a freeze can reach.

Need a hand before the first cold front?

If the backflow preventer at your house has never been drained, is already weeping, or you are not sure which valve shuts it off, call B&B Landscaping & Masonry at 512.635.7701 or send a request. A licensed irrigator can walk the system with you, mark the valves, and get it ready before Georgetown's first hard freeze.