The single most common cause of costly spring repairs at Ontario cottages is water left in the plumbing system over winter. A pipe that freezes and splits — whether in the crawlspace, behind a wall, or in the pump house — can release hundreds of litres of water when it thaws in spring. The damage is often invisible until someone opens the cottage in May and finds warped floors or a collapsed ceiling.
Winterizing a water system is not technically complicated, but it requires a specific sequence. Doing steps out of order leaves water in places the process was intended to clear. The procedure also differs depending on whether the cottage draws from a lake intake or a drilled well, and whether the system uses a submersible pump or a jet pump.
Before Starting: What You Need
- An air compressor capable of reaching 30 to 50 PSI — a small portable unit is sufficient for most cottage plumbing systems
- A blowout adapter that fits the service port on the pressure tank or pump inlet (standard garden hose thread works for most Ontario-era systems)
- Propylene glycol antifreeze, non-toxic, rated to at least -40°C — available at most hardware and automotive stores in cottage country
- A bucket and a sponge for the toilet bowl
- A flashlight and access to the pressure tank, all shut-off valves, and the water heater
Do not use automotive antifreeze (ethylene glycol) in any plumbing system. It is toxic and can contaminate well casings and the surrounding soil. Non-toxic propylene glycol is the standard choice for cottage drain traps and toilet bowls.
Step 1: Shut Off the Water Source
For a lake intake system, close the intake ball valve at the point where the pipe enters the building. If the intake pipe runs through the lake bed rather than along the surface, it may already be below the freeze line and doesn't require draining — but the portion of pipe that runs above ground or through an unheated space must be cleared.
For a drilled well with a submersible pump, turn off the pump breaker at the electrical panel first. The well casing itself will not freeze — drilled wells in Ontario typically extend well below the frost line — but the pressure tank, the lines between the well head and the pressure tank, and all above-grade distribution lines must be drained.
Step 2: Shut Off the Water Heater
Turn off the water heater — electric, propane, or oil — before draining the system. A water heater that continues to run after the supply is closed will overheat the element or the gas pilot assembly within minutes. Allow the heater to cool before draining it. Most tank-style heaters have a drain valve at the base; attach a garden hose and run it to a floor drain or outside.
Step 3: Open All Taps and Valves
Open every faucet in the cottage — kitchen, bathroom, laundry sink — to the open position. Open the toilet supply valve. Open any outdoor hose bibs. This releases the pressure in the system and allows air to enter as water drains down.
Leave the taps open throughout the blow-out process. A closed tap creates a sealed section that the air pressure cannot clear.
Step 4: Drain the Pressure Tank
Most Ontario-era cottages have a steel or fibreglass pressure tank in the basement, utility room, or pump house. Locate the drain valve on the tank and open it. If the tank is waterlogged — meaning it has lost its air charge — the water will drain slowly or not at all until you release the air pressure charge at the Schrader valve on top of the tank.
A properly functioning pressure tank with a bladder will drain quickly once the system pressure is released. A waterlogged tank that has lost its bladder integrity may need to be partially drained by pump-out or may require replacement — a task worth scheduling before closing if the tank is cycling abnormally frequently during the summer.
Step 5: Blow Out the Lines
Connect the air compressor to the blowout port on the pressure tank or at the pump inlet. Set pressure to 30 PSI — enough to move water through the pipes without risking joint failure. Higher pressures are not more effective and can damage fittings in older systems.
Work through the cottage methodically. Start at the fixture closest to the supply and work toward the farthest point from the inlet. Apply air for 15 to 30 seconds at each fixture, then move to the next. Repeat the circuit twice. Most above-grade lines in a simple cottage system are fully cleared within 20 to 30 minutes.
Key locations that require specific attention:
- The pump itself: If the cottage uses a jet pump (above-ground), it has a water-primed impeller housing. This must be drained through the drain plug at the base of the pump — air pressure alone will not clear it.
- The hot water lines: Hot water supply lines run from the water heater to each fixture. These are separate from the cold supply and must be blown out independently once the heater is drained.
- Any branch lines to an outdoor shower or hose bib on a deck: These short branches are easy to miss and the first to freeze.
Step 6: Add Antifreeze to Drain Traps
Every P-trap in the cottage — under every sink, in every floor drain — holds a small amount of standing water by design. That water is what creates the seal that prevents sewer gas from entering the building. Blowing air through the system will not remove this standing water.
Pour approximately 250 mL of non-toxic propylene glycol antifreeze into each drain after blowing out the lines. Tilt the bottle so it flows into the trap rather than straight down the pipe. The antifreeze will displace the water in the trap or mix with it sufficiently to lower the freeze point below the winter temperatures the cottage will experience.
For the toilet, sponge out as much water as possible from the bowl and the tank. Then pour antifreeze into both — approximately 500 mL in the bowl to protect the trap at the base of the toilet, and enough in the tank to cover the flush valve assembly.
Step 7: UV Filter Storage
If the cottage water system includes a UV disinfection filter — which is standard practice on properties with lake intakes in Ontario — the UV bulb and quartz sleeve must be removed for winter. Leaving them in a flooded housing that freezes will crack the quartz sleeve, which costs roughly $80 to $140 to replace, and may damage the UV lamp.
Remove the bulb and sleeve after the system is drained. Store both in a dry location — the original packaging works well. Note the installation date on the lamp. Most manufacturers specify annual replacement regardless of run hours, and closing day is a logical time to assess whether the bulb is due for replacement before spring startup.
Step 8: Label and Document
Before leaving the property, walk through the cottage and confirm that every tap is left in the open position and every shut-off valve is closed. A quick diagram or note on the inside of the electrical panel door — listing which valves are closed and which circuit breakers are shut off — saves considerable time and confusion when returning in spring.
If the property has a water softener, it will require its own winterization procedure. Most resin-bed softeners have a bypass valve; engage the bypass, then flush and drain the brine tank. Consult the equipment manual for the specific procedure, as the drain and rinse steps differ between brands.
Timing
In most of central and southern Ontario — Muskoka, Haliburton, Kawartha, Hastings — the safe window for winterization is the last week of September through the Thanksgiving long weekend in October. Properties north of Parry Sound or in the Algonquin highlands should consider completing the procedure in mid-September, as sustained below-zero overnight temperatures can arrive earlier at those elevations.
The Ontario MNRF publishes seasonal data on lake levels and ice conditions that can be useful for timing both the fall close-up and the spring opening.