The Mix

Mixing drinking water storage tanks is well recognized as an important tool for improving water quality and protecting tank assets. There are many mixing technologies for operators to choose from, with varying degrees of performance, but to solve serious water quality problems, powerful mixing is key.

Powerful active mixing eliminates thermal stratification and ensures uniform conditions throughout the tank. This has been shown to lower overall disinfectant residual demand, reduce the risk of nitrification and enable safe, reliable boosting of residual disinfectant. Additionally, powerful mixing can protect and preserve tank assets by preventing the ice formation (which can scrape tank coatings or puncture tanks), and lowering summertime headspace temperatures (which reduces corrosion rates).

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.

Just as electronic technologies have improved with time, technologies in the water distribution system have evolved from large and expensive pieces of equipment into smaller and more efficient solutions. Developed in the ‘80s, passive mixing systems use bulky nozzles with one-way valves to squirt water in different directions during the fill cycle. Because these mixers rely on the momentum of influent water, passive systems do not mix water once the tank is full or during the drain cycle and tanks re-stratify once the infill has stopped. A common workaround is forcing tank operators into a minimum turnover rate (which is both energy-intensive and expensive).