Every winter, water utilities across the United States and Canada deal with the challenges of cold weather, including main breaks and equipment outages. While these emergencies come without warning, they are obvious and visible when they do occur. But in other parts of the water distribution system, cold weather can create risk that is hidden from view: ice formation inside water storage tanks.

Often, the only time operators realize they have a problem with ice in their tanks is when it’s too late: after a tank’s interior is damaged or when the tank wall is punctured. Few operators climb and inspect their tanks in winter, so the extent of ice formation inside of water storage tanks is often unknown. Below we have compiled five factors that indicate your tank is at risk for ice formation.

1. Low R-Value. Tanks with a low r-value, or poor insulation, are more vulnerable to freezing temperatures and heat loss. Concrete and underground tanks typically have a higher r-value and are less prone to ice formation.
2. Tank Shape. Tanks with a high surface area to volume ratio, such as a standpipe, are more susceptible to ice formation. It is very challenging to force warm water entering the tank up to the top layers of a standpipe to prevent ice.
   
3. Surface Water. Utilities using surface source water will experience greater water temperature swings during the year, and greater propensity for ice formation in tanks. During the winter, the temperature of surface water entering the tank can fall to close to freezing.
   
4. Low turnover. Tanks with little to no turnover, such as tanks used for fire protection, are at a greater risk for ice formation. It is important to have the warm water entering a tank mixing with the rest of the volume to prevent ice at the top of the tank.
   
5. Poor Mixing. Water coming into the tank between 32-40° is actually denser than ice water and will remain at the bottom of the tank unmixed. This causes freezing water to float to the top of the tank and form ice. Active mixing forces the warmer, denser water on the floor of the tank up to the top, and keeps all the water in the tank at a constant temperature.