Charles Fishman (author of The Big Thirst) wrote a piece for the Washington Post last month on “Five Myths About Water.” Number two on Charles’ myth list is “bottled water is better than tap water,” where he unveils that tap water is actually MORE closely monitored than bottled water and that in blind taste tests “people can’t reliably pick bottled from tap.” At PAX Water, Charles’ article got us thinking about some of the myths we’re trying to bust in the drinking water industry. Here are our top five:

1. Myth – High turnover storage tanks don’t stratify

• Reality – Forcing high turnover in tanks is a common workaround used by utilities to manipulate hydraulics and “mix” a tank. However, the temperature data inside a tank shows that deep cycling, even up to 60%, still leaves thermal stratification in the top layers. Not only does high turnover not adequately mix the tank, it also creates high operational costs.

2. Myth – Separating the inlet and outlet is a good mixing solution

• Reality – Separating the inlet and the outlet is NOT a mixing solution – it’s just the opposite. A well-mixed tank has the same water quality everywhere – it shouldn’t matter where your outlet is. Separating your inlet and outlet suggests that your water quality is not the same throughout your tank, and depending on their configuration, separate inlets and outlets may actually impede mixing. This mistake is being perpetuated by regulators in a number of states. Instead of talking about separate inlets and outlets, they should be talking about tanks being well-mixed at all times. Fortunately, some state regulators are accepting active mixers in lieu of separate inlets/outlets. That’s a good thing too, as separating your inlet and outlet is a costly tank retrofit.

3. Myth – The PAX Water Mixer doesn’t mix below the impeller

• Reality – It’s true that some mixers on the market don’t have enough power to fully blend water inside a tank – leaving tanks vulnerable to thermal stratification. PAX Water uses temperature probes (the lowest one typically installed within 1 foot of the tank floor) to demonstrate both the blend time and temperature homogenization created by active mixing. For example, the PAX Water Mixer was able to fully blend a 500,000 gallon tank in Redwood City, CA within three hours, from the base of the tank to the upper surface.

4. Myth – There’s a decrease in mixing away from the impeller

• Reality – One good way to gauge whether or not a mixer’s performance decreases away from the impeller is to look at how it performs inside a standpipe – perhaps the most challenging tank geometry to mix. Temperature data from a 127 foot tall tank in Spanaway, Washington busts this myth. The PAX Water Mixer was able to completely mix the initially stratified column of water in seven days – resulting in a temperature decrease (from 66°F to 61°F) at the surface and a concurrent residual increase (from 0.00 mg/L to 0.31 mg/L).

5. Myth – Passive mixers require less maintenance than active mixers

• Reality – A passive mixing system is a fixed, permanent installation that involves multiple nozzles and piping. This design puts an extra burden on pumps in the distribution system and creates more surface area (and bolts and corrosion points) to paint, coat and maintain inside the tank. This system is also very expensive to design and install and requires extra time, labor and money to maintain. By contrast, active mixing systems are less expensive, easier and faster to install (half-day installation without cranes or needing to drain the reservoir) and can be easily removed during tank maintenance.  Active mixers can also be used to meet state requirements for a “separate inlet/outlet” – thus displacing a huge piping and construction cost.