How Do You Drain a Sprinkler System? Winter Drainage Steps

Introduction

If you own a residential or commercial irrigation system, you’ve likely asked yourself: How Do You Drain a Sprinkler System? before the cold winter months set in. Proper drainage is one of the most critical maintenance tasks for protecting your investment, as frozen water left in pipes, valves, and sprinkler heads can cause catastrophic, costly damage. Whether you live in a region with harsh, sustained freezing temperatures or a milder climate with occasional cold snaps, taking the time to fully drain your system before winter arrives will save you hundreds or even thousands of dollars in repair costs come spring. This comprehensive guide walks you through every step of the process, explains the most common drainage methods, highlights tools you’ll need, and shares expert tips to avoid common mistakes that lead to broken irrigation components.

• Why Draining Your Sprinkler System Is Non-Negotiable
• How Do You Drain a Sprinkler System? Key Methods Explained
• Step-by-Step Guide to Manual Drainage
• Step-by-Step Guide to Automatic Drainage
• Step-by-Step Guide to Blowout Drainage
• Comparison of Sprinkler System Drainage Methods
• Tools and Equipment You’ll Need
• Common Mistakes to Avoid When Draining Your Sprinkler System
• Tips for Maintaining Your Sprinkler System Year-Round
• Frequently Asked Questions
• Conclusion

Why Draining Your Sprinkler System Is Non-Negotiable

Water expands by approximately 9% when it freezes, a fact that makes un-drained sprinkler systems extremely vulnerable to cold weather damage. When water left in underground or above-ground pipes freezes, it exerts immense pressure on the walls of the pipes, which can cause them to crack or burst entirely. This damage isn’t limited to pipes: frozen water in backflow preventers, control valves, and sprinkler heads can warp seals, break internal components, and render the entire system inoperable.

Repairing a frozen, damaged sprinkler system can cost anywhere from $200 for a single broken pipe to $5,000 or more for full system replacement, depending on the extent of the damage. Even small cracks in pipes can lead to water waste, soggy lawn areas, and higher water bills once temperatures rise and the system is turned back on. For most homeowners, the 30 to 90 minutes it takes to properly drain a sprinkler system is a tiny time investment compared to the cost of repairs. Even if you live in a region with mild winters, unexpected cold snaps with temperatures dropping below 32°F (0°C) can cause damage, making annual drainage a smart precaution for any irrigation system owner.

How Do You Drain a Sprinkler System? Key Methods Explained

There are three primary methods for draining a sprinkler system, each suited to different climates, system types, and homeowner preferences. The method you choose will depend on whether your system has built-in automatic drains, how cold your winters get, and whether you have access to compressed air equipment. Understanding the pros and cons of each method will help you select the best option for your needs to ensure all standing water is removed from the system.

Manual Drainage

Manual drainage is the simplest, lowest-cost method, ideal for systems with clearly marked drain valves at the lowest points of the irrigation lines. It works by opening these valves to let gravity pull standing water out of the pipes, then closing the valves once the system is empty. This method is best for homeowners in mild winter climates where temperatures rarely stay below freezing for extended periods.

Automatic Drainage

Automatic drainage systems are equipped with factory-installed drain valves that open automatically when water pressure in the lines drops below a certain threshold, usually when the main water supply is turned off. These valves require minimal effort to activate, but they can fail over time due to debris buildup, wear, or improper installation, so they should always be checked after activation to confirm all water has drained.

Blowout Drainage

Blowout drainage uses compressed air to force all remaining water out of the sprinkler lines, making it the most effective method for cold climates with sustained freezing temperatures. This method requires an air compressor with a pressure regulator to avoid damaging the system’s components, and it takes slightly more time and equipment than manual or automatic drainage, but it eliminates the risk of leftover water freezing in hard-to-reach parts of the system.

Step-by-Step Guide to Manual Drainage

Manual drainage is a straightforward process that most homeowners can complete in 30 to 60 minutes with basic tools. Follow these steps to ensure all standing water is removed from your system:

1. Shut off the main water supply to the sprinkler system. Locate the main shut-off valve, usually near your home’s water meter or the backflow preventer for the irrigation system. Turn the valve fully clockwise to stop all water flow to the sprinkler lines. This step is critical to prevent new water from entering the system while you drain it.
2. Locate and open all manual drain valves. These valves are typically installed at the lowest points of your irrigation lines, often at the ends of lateral lines or near the backflow preventer. Use an adjustable wrench to turn the drain valves counterclockwise to open them. If you can’t locate your drain valves, check your system’s installation manual or look for small, capped pipes near the lowest points of your lawn.
3. Open 2 to 3 sprinkler heads in the lowest areas of your lawn. This allows air to flow into the pipes, which helps gravity pull standing water out through the open drain valves more efficiently. Choose heads that are at the lowest elevation on your property for best results.
4. Let the system drain completely. Allow 15 to 30 minutes for all standing water to flow out of the pipes. Check the drain valves to confirm water is no longer dripping out, and use a bucket to catch any residual water if needed. If you notice standing water in the pipes after 30 minutes, check for clogs in the drain valves or low spots in the lines that are trapping water.
5. Drain the backflow preventer. Most backflow preventers have built-in drain valves or caps that can be removed to let water out. Consult your backflow preventer’s manual for specific instructions, as models vary. Failing to drain the backflow preventer is one of the most common causes of winter damage to sprinkler systems.
6. Close all drain valves once the system is fully empty. Turn each drain valve clockwise to close it tightly, preventing debris or small animals from entering the pipes over the winter. If you have automatic drain valves, confirm they are closed as well to avoid leaks when the system is turned back on in spring.

Step-by-Step Guide to Automatic Drainage

If your sprinkler system is equipped with automatic drain valves, the drainage process is even faster, but it still requires a few simple steps to ensure it works correctly:

1. Shut off the main water supply to the sprinkler system. Just like with manual drainage, turn the main shut-off valve clockwise to stop water flow to the lines.
2. Depressurize the system by running one zone briefly. Turn on your sprinkler controller and run one zone for 1 to 2 minutes. This drops the water pressure in the lines, which triggers the automatic drain valves to open.
3. Wait for all water to drain. Allow 10 to 20 minutes for the automatic drains to release all standing water. You can open a few sprinkler heads to confirm air is flowing through the lines, which indicates the system is fully drained.
4. Drain the backflow preventer separately. Automatic drain valves do not cover the backflow preventer, so you will still need to drain this component manually to avoid damage.
5. Close any manual drain valves if present. If your system has both automatic and manual drain valves, close the manual valves to prevent leaks when the system is reactivated in spring.

Step-by-Step Guide to Blowout Drainage

Blowout drainage is the most reliable method for cold climates, but it requires careful execution to avoid damaging your sprinkler system. Follow these steps closely to safely remove all water from your lines:

Safety Note: Always wear eye protection and gloves when performing a blowout. Never exceed 80 PSI for residential sprinkler systems, as higher pressure can crack pipes, damage sprinkler heads, and ruin valves. Do not use an oil-lubricated air compressor, as oil can damage the internal components of your irrigation system.

1. Shut off the main water supply to the sprinkler system. Turn the main shut-off valve clockwise to stop all water flow. Leave the controller on for now, as you will need it to activate each zone individually.
2. Attach the air compressor hose to the blowout port. The blowout port is usually located on the side of the backflow preventer, or you may need to remove the cap from the main line to access it. Use a hose adapter that fits both your compressor and the blowout port to create a tight seal.
3. Set the air compressor pressure to 50-80 PSI. Residential sprinkler systems are designed to handle up to 80 PSI, so never set the regulator higher than this. Higher pressure can cause irreversible damage to pipes and components.
4. Activate the first sprinkler zone using the controller. Turn on the first zone, then turn on the air compressor. You will see water spraying out of the active sprinkler heads first, followed by mist, and then only air. Once only air is coming out of the heads, turn off the zone and move to the next one.
5. Repeat the process for each sprinkler zone. Go through each zone one by one, blowing out all water until only air is released. Do not run the compressor for more than 1 to 2 minutes per zone without a break, as excessive air flow can overheat the compressor and damage system components.
6. Drain the backflow preventer and main line. Once all zones are blown out, turn off the compressor and disconnect the hose. Open the main drain valve for the backflow preventer and main line to let any remaining water out. You can also open a few sprinkler heads to confirm no water is left in the lines.
7. Close all valves once the system is fully drained. Close the main drain valve and any manual drain valves to prevent debris from entering the system over the winter.

Comparison of Sprinkler System Drainage Methods

Choosing the right drainage method for your system depends on your climate, budget, and the type of irrigation system you have. The table below breaks down the key differences between the three most common drainage methods to help you make an informed decision:

Tools and Equipment You’ll Need

The tools you need to drain your sprinkler system will vary depending on the method you choose, but most homeowners will only need a few basic items:

• Adjustable wrench: For opening and closing manual drain valves and removing caps from the backflow preventer.
• Air compressor with pressure regulator: Required for blowout drainage. You can rent a compressor from most home improvement stores for $30 to $100 per day if you don’t own one. Make sure the compressor is oil-free to avoid damaging your irrigation components.
• Hose adapter: To connect the air compressor hose to the blowout port on your backflow preventer. Adapters are available at most hardware stores for $5 to $15.
• Eye protection and work gloves: Essential for blowout drainage to protect your eyes from flying water and debris, and your hands from cold water and sharp pipe edges.
• Bucket and towels: For catching water from drain valves and cleaning up spills.
• System installation manual: Helpful for locating drain valves, blowout ports, and specific instructions for your backflow preventer model.

Common Mistakes to Avoid When Draining Your Sprinkler System

Even small errors during the drainage process can lead to costly damage or an incomplete drain that leaves water in your lines. Avoid these common mistakes to ensure your system is properly protected over the winter:

Mistake 1: Forgetting to Shut Off the Main Water Supply

Failing to turn off the main water supply before opening drain valves or using an air compressor can cause new water to flow into the lines while you’re draining, leading to standing water left in the pipes. Always shut off the main supply first, and confirm it is fully closed by turning on a sprinkler head briefly to check for water flow.

Mistake 2: Using Excessive Air Pressure During Blowout

Using an air compressor set to more than 80 PSI can crack PVC pipes, damage sprinkler heads, and ruin valve seals. Always use a pressure regulator to keep pressure within the safe range for your system, and check your system’s manual for the maximum recommended PSI if you’re unsure.

Mistake 3: Neglecting to Drain the Backflow Preventer

The backflow preventer is one of the most vulnerable components to freeze damage, as it holds a large volume of water even after the rest of the system is drained. Always drain the backflow preventer separately, following the instructions in its manual, to avoid cracked seals and broken internal parts.

Mistake 4: Closing Drain Valves Before All Water Is Removed

Closing drain valves too early can trap small amounts of water in low spots in the lines, which can freeze and cause cracks over time. Wait until all water has stopped dripping from the drain valves before closing them, and double-check by opening a few sprinkler heads to confirm no water is left.

Mistake 5: Skipping Annual Inspections of Drain Valves

Manual and automatic drain valves can become clogged with debris, rust, or mineral buildup over time, preventing them from opening fully when needed. Inspect all drain valves in the fall before you drain the system, and clean or replace any that are faulty to ensure they work correctly when temperatures drop.

Tips for Maintaining Your Sprinkler System Year-Round

Proper maintenance outside of the winter drainage process will extend the life of your sprinkler system and reduce the risk of damage each year. Follow these expert tips to keep your system in top condition:

• Insulate above-ground pipes and valves with foam sleeves to protect them from freezing temperatures, especially if they are located in uninsulated areas like garages or crawl spaces.
• Mark all drain valve locations in the fall with small flags or paint so you can find them easily when it’s time to drain the system.
• Test automatic drain valves annually by depressurizing the system to confirm they open and drain water correctly, replacing any faulty valves before winter.
• Inspect the entire system in spring before turning it back on to check for broken heads, leaking pipes, or damaged valves, and repair any issues before use.
• Set your sprinkler controller to rain mode for the winter if it is located in an uninsulated area, and cover it with an insulated blanket if temperatures are expected to drop well below freezing.

Frequently Asked Questions

How often do I need to drain my sprinkler system?

You only need to drain your sprinkler system once per year, before the first expected freeze in the fall. If you live in a mild climate with no sustained freezing temperatures, you may be able to skip draining in some years, but it is always recommended to drain the system annually to avoid damage from unexpected cold snaps. Even a single night of temperatures below 32°F (0°C) can cause frozen water to crack pipes if the system is not drained.

Can I use a leaf blower instead of an air compressor to blow out my sprinkler lines?

No, leaf blowers are not suitable for blowing out sprinkler lines. They do not produce consistent, regulated air pressure, and their output is often too high or too low to effectively remove water without damaging the system. Leaf blowers also do not have a pressure regulator, so they can easily exceed the 80 PSI maximum recommended for residential sprinkler systems, leading to cracked pipes and broken components. Always use a dedicated air compressor with a pressure regulator for blowout drainage.

What if I forget to drain my sprinkler system before a freeze?

If you forget to drain your system and temperatures drop below freezing, turn off the main water supply to the sprinkler system immediately to prevent more water from entering the lines. Wait until temperatures rise consistently above freezing, then drain the system as soon as possible to minimize damage. Once the system is drained, inspect all pipes, valves, and sprinkler heads for leaks, cracks, or broken parts, and repair any issues before turning the system back on in spring. If you notice significant damage, contact a professional irrigation technician to assess and repair the system.

Do I still need to drain my sprinkler system if I have automatic drain valves?

Yes, you still need to take steps to drain your system even if you have automatic drain valves. Automatic valves are designed to open when water pressure drops, but they can fail due to debris buildup, wear, or improper installation. It is important to manually verify that all water has drained from the lines after the automatic valves activate, and to always drain the backflow preventer separately, as automatic drains do not cover this component. Relying solely on automatic drains without verification can leave standing water in the system that freezes and causes damage.

Is winterizing a sprinkler system the same as draining it?

Draining is a core part of winterizing a sprinkler system, but the two terms are not interchangeable. Draining refers specifically to removing all standing water from the pipes, valves, and sprinkler heads to prevent freeze damage. Full winterization includes additional steps to protect the system from cold, such as insulating above-ground pipes, covering exposed valves, shutting off the controller, and shutting off the main water supply. For maximum protection, especially in cold climates, you should complete both the drainage process and additional winterization steps each fall.

Conclusion

Knowing How Do You Drain a Sprinkler System? is an essential skill for any homeowner with an irrigation system, as proper drainage is the single most effective way to prevent costly cold-weather damage. Whether you choose manual drainage for a mild climate, rely on automatic drains for convenience, or use blowout drainage for harsh winters, following the step-by-step guides outlined in this article will ensure all standing water is removed from your system before temperatures drop below freezing. Avoiding common mistakes like forgetting to drain the backflow preventer or using excessive air pressure will further reduce your risk of damage, and regular year-round maintenance will extend the life of your system for years to come. Taking 30 to 90 minutes each fall to drain your sprinkler system is a small time investment that will save you hundreds or thousands of dollars in repair costs, and keep your lawn looking lush and healthy when spring arrives.