Sprinkler Blowout in Colorado: How to Winterize Your Sprinkler System

Water expands by about one-eleventh when it freezes, according to CSU Extension. That's enough to split pipe, crack valves and break the backflow preventer by the side of the house. Most of that damage stays in the yard and waits for spring. But where the supply line, shutoff or backflow device sits in a basement, crawl space or along the foundation, a frozen fitting can leak into the house. If that has already happened, Reestorian can connect you with a local provider for burst and frozen pipe water damage in Littleton.

This is general information. A blowout uses high-pressure air, so if you're unsure about any step, hire an irrigation professional.

What is a sprinkler blowout?

A blowout is the last step of winterizing. After the water supply to the system is shut off, an air compressor is connected to the irrigation line and each zone is run in turn, so air pushes the remaining water out through the sprinkler heads. CSU Extension calls a professional blowout the preferred method, though a homeowner with the right compressor and pressure regulation can do it.

When to do a sprinkler blowout in Colorado

Colorado fall weather makes timing tricky. CSU Extension's PlantTalk notes that temperatures can swing widely between day and night, so you're balancing freeze risk against a dry lawn.

A Denver irrigation pro told 9NEWS he tries to get systems shut off by Nov. 1, or the first or second week of November. Platte Canyon Water and Sanitation District in Littleton says it gets several calls about frozen or broken irrigation lines around this time of year, and that shutting off a little early shouldn't hurt the lawn.

Also check your water provider's current rules. In fall 2025, for example, Bow Mar Water and Sanitation District in Littleton reminded customers that Denver Water's Stage 1 drought rules banned lawn watering after Sept. 30.

How to winterize a sprinkler system

These steps follow CSU Extension's fact sheet. Every system is different, so check your owner's manual too.

• Shut off the water supply. Close the valve that feeds the irrigation system. On many Colorado homes it's a stop-and-waste valve that CSU says may be about 5 feet underground and needs a long key. Don't force it. Others are inside, in a basement or crawl space.
• Turn the controller to off or rain mode. Leave it plugged in.
• Drain the backflow preventer the right way for its type (see below).
• Connect the compressor to the blowout fitting downstream of the backflow preventer, and close the isolation valve between them. If there's no blowout fitting, have one added.
• Set a regulated pressure. Keep it within CSU's range: 40 to 80 psi, no more than 80 for rigid PVC and no more than 50 for flexible polyethylene.
• Blow out one zone at a time. Run each zone from the controller and let air push water out until only mist comes from the heads.
• Go around twice with short cycles. CSU says to blow each zone out twice and not to keep running air through a zone that's already dry.
• Leave valves half open after the blowout, as CSU describes, and insulate any parts above ground.

How much psi for a sprinkler blowout?

More pressure isn't better. CSU warns that too much pressure can blow nozzles off and damage the system. Air running through a dry line also creates friction, which can heat pipes and fittings enough to weaken or melt them.

What size air compressor do you need?

CSU Extension's rule of thumb: divide each zone's flow, in gallons per minute, by 7.5 to get the cubic feet per minute (CFM) of air needed.

A compressor that's too small takes longer and works harder. Too much volume can pressurize the lines too fast, which is why a regulator at the outlet matters. A simple check from CSU: if the heads stay popped up while air is flowing, the compressor is keeping up.

Protecting the backflow preventer

The backflow preventer keeps irrigation water from flowing back into your drinking water. It's often the most exposed part of the system, standing above ground by the foundation. CSU Extension describes different handling for each common type:

Then insulate it. Platte Canyon and Bow Mar water districts both advise insulating above-ground backflow preventers and valves. PlantTalk suggests insulation covered with plastic, wrapped down to ground level and secured with duct tape.

Can you winterize a sprinkler system without a blowout?

Some systems have manual or automatic drain valves at low points. CSU Extension doesn't recommend relying on them alone. Buried pipe can settle into low spots over the years, and you can't see whether the lines are truly empty. PlantTalk adds that blowing the lines out helps even when drains are present, and CSU says lines with electric valves have to be blown out with air.

Sprinkler blowout safety

• Wear eye protection. Fittings and nozzles are under pressure.
• Never stand over a head, valve box or backflow device while air is flowing.
• Don't exceed the pressure limits in the table above.
• Keep pets inside. CSU notes the whistling can upset them.
• Don't run air through a dry zone. The heat can damage pipe.
• Never blow air through a PVB.

How much does a sprinkler blowout cost?

Reestorian doesn't set or publish prices for irrigation work. What you'll pay depends on the number of zones, the type of backflow preventer, whether the shutoff is hard to reach and whether any repairs are needed. Ask for the price per visit and whether it includes spring startup. Compare it with the cost of a cracked backflow preventer or a split line, and with water damage inside if a fitting near the house fails.

What to do if a sprinkler line froze anyway

• Outside: look for a split backflow body, water bubbling up in the yard or a valve box full of water in spring. Turn the irrigation supply off and call an irrigation pro.
• Inside: if the irrigation supply runs through a basement or crawl space, check the pipe and shutoff for drips after the first hard freeze and again when you restart in spring. A cracked fitting there can soak framing, insulation and drywall.
• When you restart: CSU says to close the test cocks and ball valves first, then open the main valve slowly to avoid water hammer, and watch for leaks.

InterNACHI's life expectancy chart lists sprinkler heads at about 10 to 14 years and irrigation valves at about 20. Older parts are more likely to crack, so spring startup is a good time to inspect them.

Protect the rest of the house, too

The same cold that freezes sprinkler lines can freeze hose bibs and pipes in outside walls. While you winterize the irrigation, disconnect garden hoses, shut off and drain outside faucets if they aren't frost-free, and follow the checklist to prevent frozen pipes. If a pipe does split, the burst pipe first-hour steps show what to do right away.

Related reading: Get the full checklist to prevent frozen pipes, and learn at what temperature pipes freeze in Colorado homes.

When should you call a water damage professional?

Call a professional when:

• A frozen irrigation line, shutoff or backflow fitting leaked into a basement, crawl space or wall
• Water soaked drywall, insulation or carpet near where the irrigation supply enters the house
• You smell mustiness near the foundation after a freeze
• You need moisture readings and photos for an insurance claim

Sprinkler line froze and leaked in Littleton? Call (928) 394-5135 to reach a local water damage provider.