How to Drain a Sprinkler System Before Winter

Understanding Water Removal in Irrigation Systems

As temperatures drop during colder months, irrigation system owners face a critical maintenance challenge. Water contained within sprinkler systems, backflow preventers, and underground pipes poses a significant risk when exposed to freezing conditions. The fundamental problem stems from the physical properties of water: when it freezes, it expands with tremendous force, capable of cracking steel components and shattering plastic fittings. This expansion creates internal pressure that can damage valves, pipes, and specialized equipment throughout the entire system.

The process of removing this water before winter arrives is commonly referred to as bleeding or draining the system. This preventative maintenance procedure is one of the most effective ways to safeguard your irrigation investment and avoid expensive repairs or complete system replacement come spring.

Why Winter Drainage Is Critical for System Longevity

Water remaining in any part of your sprinkler infrastructure becomes hazardous once temperatures dip below freezing. The expansion force created by frozen water is remarkably powerful—capable of generating enough pressure to rupture even reinforced steel components. Backflow preventers, which contain multiple internal chambers and plastic components, are particularly vulnerable. A single freeze cycle can permanently damage these devices, rendering them non-functional and requiring professional replacement.

Beyond the backflow preventer, water trapped in mainlines, zone lines, and valve bodies throughout the system can freeze and expand, creating blockages or cracks that may not be immediately apparent. When spring arrives and you attempt to activate the system, you may discover that sections of pipe have been compromised or that connections have developed leaks.

The financial implications of ignoring this maintenance step are substantial. A damaged backflow preventer alone can cost hundreds of dollars to replace. Multiple burst pipes throughout the system could require thousands in repairs. In contrast, spending an hour or two performing drainage procedures costs virtually nothing and protects your entire investment.

Preparing Your System: Essential First Steps

Before beginning the drainage process, gather the necessary tools and materials. You will need:

• Adjustable wrench or pliers
• Flathead screwdriver
• Bucket or container for water collection
• Cloth or towels for cleanup
• Safety glasses
• Work gloves

Turn off all water supply to the sprinkler system at the main shutoff valve, which is typically located where the irrigation line branches off from your home’s main water supply. Locate this valve and turn it fully perpendicular to the pipe direction—this ensures water stops flowing into the system. It is also advisable to turn off the irrigation controller or timer, which prevents accidental activation during the drainage process.

Identify all components that require drainage. This includes the backflow preventer (if your system includes one), the main supply line, all zone valves, and any low-point drain valves that may exist throughout the system. Most residential systems have test cocks—small valves with removable caps—that serve as drainage points.

The Backflow Preventer: Anatomy and Drainage Procedure

The backflow preventer is a specialized device installed to comply with building codes and protect municipal water supplies from contamination. It contains multiple internal chambers separated by check valves and relief mechanisms. Understanding its basic structure helps explain why proper drainage is essential.

A typical residential backflow preventer (pressure vacuum breaker model) has two isolation ball valves—one on the supply side and one on the downstream side toward your sprinklers. Between these valves are small test cocks with removable plastic caps. These test cocks are specifically designed as drainage points.

Begin the drainage procedure by fully closing both isolation valves. The supply-side valve controls water entering the device, while the downstream valve controls water exiting toward your sprinklers. Close these by turning them until they sit perpendicular to the pipe—essentially creating a quarter-turn to the horizontal position.

Once both isolation valves are closed, carefully remove the plastic caps from all test cocks. Have your bucket ready, as water may spray out. Using your flathead screwdriver, gently turn the uppermost test cock counterclockwise approximately one-quarter to one-half turn. Water will begin flowing out, releasing the internal pressure. Continue turning until water stops flowing freely, then leave it open.

Move to the next test cock and repeat this process. Typically, a backflow preventer has two or three test cocks requiring drainage. With the main test cocks open, you have now released the trapped water and internal pressure. Allow several minutes for all remaining water to drip out—do not rush this step.

Completing the Drainage: Zone Valves and Main Lines

After the backflow preventer is drained and test cocks are open, you must address water remaining in the main supply line and individual zone lines. Open any manual drain valves located at the lowest points of your system. These are typically found at the end of the mainline or at the bottom of each zone line.

If your system includes manual shutoff valves at individual zones, slowly open these as well. Do not open them rapidly, as this can cause water hammer—a sudden surge of pressure that can damage fittings and joints. Gradual opening allows water to flow out smoothly without shock stress on the system components.

For systems without dedicated low-point drains, you may need to slightly loosen compression fittings at the lowest accessible points to allow residual water to escape. Wrap a cloth around the fitting before loosening it to contain any spray, then tighten it again once drainage ceases.

Allow the system to drain completely. This may take 15 to 30 minutes depending on the total volume of water and the number of drainage points. Some water will continue dripping slowly even after the main flow stops—this is normal and expected.

Sealing the System: The Final Configuration

Once all water has drained, you must position all valves and test cocks to prevent water from re-entering the system during winter. This final step is crucial because even small amounts of remaining water can freeze and cause damage.

Close all test cocks by turning them clockwise until they seat firmly. Do not over-tighten, as this can strip the delicate threads. Replace all plastic caps on the test cocks to keep debris out during the winter months.

Position both isolation valves (supply and downstream) at a 45-degree angle—neither fully open nor fully closed. This positioning prevents water from becoming trapped in the valve bodies while allowing any residual water that might freeze in the pipes to escape without building dangerous pressure.

The 45-degree angle is important because it takes advantage of the valve’s design. At this angle, the internal check mechanism does not create a complete seal, allowing trapped water to find an escape route if it begins to freeze and expand.

Additional Winter Protection Measures

While drainage is the primary defense against freeze damage, additional protection can provide extra insurance. If your backflow preventer or other above-ground components are exposed to the elements, consider wrapping them with insulation materials such as foam pipe insulation or old blankets. This reduces heat loss and may prevent water from freezing even if small amounts remain.

Some homeowners apply weather-resistant tape or plastic wrap over the entire backflow preventer assembly for additional weather protection. This is particularly helpful in regions that experience extreme temperature fluctuations or extended cold periods.

For systems with above-ground mainlines or exposed pipes, similar insulation wrapping can be beneficial. Pay special attention to pipes that pass through unheated areas such as garage walls or exterior walls of the home.

Spring Reactivation: Checking Your Work

When temperatures consistently warm in spring, it is time to reverse the drainage procedure. Before running water through the system, inspect all components for damage or leaks. Look for cracks in plastic fittings, water stains indicating seepage, or obvious breaks in pipe sections.

Slowly open the supply-side isolation valve on the backflow preventer by turning it back to align with the pipe direction. This should be done gradually—over 30 seconds or more—to allow air in the system to escape gradually. If you open it too quickly, water hammer can occur, potentially causing new damage.

Next, carefully close all test cocks by turning them clockwise until they seat firmly. Do not force them, as they are delicate components. Replace the plastic caps.

Finally, slowly open the downstream isolation valve. Again, open gradually to prevent pressure surges. At this point, water should flow through the entire system toward your sprinklers. Activate your irrigation controller and run the system through a test cycle, observing all sprinkler heads and drip lines for proper operation.

Inspect the backflow preventer and all connections for leaks. Small drips at the test cocks are normal during initial activation, but steady streams or spraying water indicate a problem requiring professional attention.

Common Mistakes and How to Avoid Them

Many homeowners compromise their winter protection efforts through preventable errors. Opening valves too quickly ranks among the most common mistakes. Rapid valve opening creates pressure surges that can damage fittings or blow water and debris through the system with force. Always open valves slowly and deliberately.

Another frequent error is failing to fully close the main supply valve. If this valve is not completely perpendicular to the pipe, water will continue trickling into the system, partially defeating the drainage effort. Double-check that your main valve is fully shut before proceeding with other steps.

Some people forget to drain zone valves or low-point drains, leaving pockets of water that can freeze and cause localized damage. A systematic approach—creating a checklist of all drainage points—helps ensure nothing is overlooked.

Failing to position isolation valves at the correct 45-degree angle after drainage is also problematic. Leaving them fully closed can trap water in the valve bodies themselves, which can then freeze and crack the valve. Leaving them fully open defeats the purpose of having isolation valves.

Professional vs. DIY Drainage Considerations

While most homeowners can successfully drain their sprinkler systems, some situations warrant professional assistance. Complex systems with multiple backflow preventers, unusual configurations, or components mounted in difficult-to-access locations may be better handled by irrigation specialists.

If your system is relatively new and under warranty, check whether performing your own drainage might void coverage. Some warranties require professional winterization to remain valid.

Additionally, if you discover damage during the inspection—such as cracked fittings, leaking connections, or malfunctioning valves—professional evaluation is advisable before attempting to operate the system again.

Frequently Asked Questions

Q: When should I drain my sprinkler system before winter?

A: Perform drainage when nighttime temperatures consistently drop to or below 32°F (0°C) and are predicted to remain cold throughout the winter season. In most climates, this occurs in late fall, typically between October and November. Do not wait until the first hard freeze, as you may miss the optimal window.

Q: What if I forget to drain the system and freezing temperatures arrive?

A: If you realize frozen conditions are imminent and you have not drained the system, perform the drainage immediately, even if a freeze is just hours away. Draining as late as possible is better than not draining at all. After the freeze ends and temperatures warm, inspect the system thoroughly for damage before attempting to operate it.

Q: Can I use compressed air to blow out my system instead of manual drainage?

A: Yes, compressed air blowout is an alternative method used by some professionals. This involves connecting an air compressor to the system and using air pressure to force water out through the sprinkler heads. However, this method requires specialized equipment, knowledge of proper pressure settings (typically 50 PSI maximum), and safety precautions. Most homeowners find manual drainage simpler and safer.

Q: Do automatic drain valves eliminate the need for manual drainage?

A: Automatic drain valves, which open when water pressure drops, are helpful but not always completely reliable. They work well for mainline drainage but may not fully empty backflow preventers or all isolated sections of pipe. Many experts recommend manual drainage as the most thorough approach, even if automatic drains are present.

Q: How can I tell if my system has freeze damage?

A: Signs of freeze damage include visible cracks in plastic fittings or pipe sections, water leaking from unusual locations when the system is running, reduced water pressure at sprinkler heads, or water spraying from unexpected points. Some damage may not be immediately obvious, so run your system slowly during spring startup and observe carefully.

Q: Is it necessary to drain if I live in a mild climate where freezing is rare?

A: If your area rarely experiences freezing temperatures, drainage may not be necessary. However, even a single unexpected hard freeze can damage your system. If freezing temperatures occur once per decade but you fail to drain that year, you may face costly repairs. Most experts recommend drainage as preventative maintenance regardless of frequency if any freezing possibility exists.