If you live in a climate where temperatures drop below freezing, Winterizing Your Rainwater Storage System is not optional—it's essential for the survival of your equipment. When water turns to ice, it expands with immense force. Without proper preparation, that expansion can shatter PVC pipes, crack costly pumps, and even rupture the thick walls of a poly tank.
To Drain or Not to Drain?
The safest way to winterize an above-ground tank in a prolonged, hard-freeze climate is to drain it completely before the first frost. If you choose this route, you must also bypass your downspouts so winter meltwater flows directly to your stormwater drains rather than refilling the tank.
However, if your winters consist of only brief freezes, or if you rely on the water year-round, complete drainage might not be practical. Large volumes of water hold a significant amount of thermal mass; a 5,000-gallon tank full of water takes much longer to freeze solid than a 50-gallon barrel. If keeping the tank full, ensure the water level is dropped by at least 10% to allow room for ice to expand upwards without pushing against the rigid top of the tank.
Protecting Pipes and Fittings
While the tank's thermal mass might prevent it from freezing completely, the thin, exposed pipes and the outlet valves will freeze very quickly. Any standing water in a pipe exposed to freezing air will turn to ice and crack the PVC. You must drain all exposed delivery pipes, hoses, and drip lines. For pipes that cannot be drained, invest in heavy-duty foam pipe insulation or electric heat tape wrapped carefully along the pipe length.
Securing the Pump
Pumps are the most expensive and fragile components of a rainwater system. A tiny amount of water left inside the pump housing will crack the internal impellers if it freezes. If your pump is installed outdoors or in an unheated shed, it is highly recommended to disconnect it entirely. Drain the pump casing according to the manufacturer's instructions, and store it indoors for the winter season.
First Flush Diverters
Don't forget the first flush diverter. This upright pipe is designed to hold the initial, dirty runoff. If it is full of water during a freeze, the pipe will burst. Leave the drip valve at the bottom fully open during winter, or better yet, remove the sealing cap entirely so water runs straight through without pooling.
Conclusion
Winterizing might seem like a chore, but taking an hour each autumn to drain pipes, insulate valves, and protect your pump will save you hundreds of dollars in repair costs come spring. Preparing your system for the cold ensures it will wake up healthy and ready to harvest the first spring showers.