Water Chemistry: Lessons Learned

It always circles back to chemistry. Managing water quality is always an exercise in manipulating chemical values so that water remains sanitized, balance and appealing.

The only way to do that, to ply the trade of the water quality professional, is be proficient in water testing. Whether it’s through traditional reagent-based tests in vials, or test strips or electronic testing technology, testing is our eyes into the chemistry of the water we’re managing. You simply cannot separate testing from water chemistry or vice versa. In a practical sense, one does not really exist without the other.

When I started in the business three decades ago, I really had very little idea what I was doing. And although I worked hard to try to find reliable information sources, they were few and far between. That was, anyway, until I started reading the Taylor Technologies Guidebook, a wonderful resource published by one of the leading manufacturers of testing technology.

By way of explaining how to test water, that single publication gave me the foundation for the entirety of pool and spa water chemical treatment. I quickly learned that through simple tests for pH, total alkalinity, calcium hardness, TDS and cyanuric acid as well as testing for combined and free available chlorine, I was able to watch the causes and effects of the chemicals I was adding. All of a sudden, I could see what a dynamic beast water chemistry can be, how it changes and reacts and how the measurable differences in chemical constituents impact each other. Through water testing, we can see how animated pools and other bodies of water become.

Even the most basic aspects of water treatment became eye opening. If I added calcium hypochlorite, I could test and see that my calcium levels and pH would increase. Then I could see in real time how, by adding acid, total alkalinity and pH would go down. Then I could see how I could elevate pH again by adding bicarbonate. Everything we do to the water has a cause and effect relationship.

It’s impossible to ascertain any of that without routine testing that is done correctly and reliably.

Later on, I discovered how important it is to test source water at the tap. To this day, I’m amazed how some people try to manage water chemistry without first understanding how the water we use to fill vessels creates a baseline that influences the chemistry going forward. I learned, for example, that water in one area can be completely different from what you find just a few miles away. Through my basic testing regimens, I learned that water in one place might change over time, meaning it’s important to never make assumptions that will always stay the same.

RELATED: Why You Need to Test Source Water at the Tap

I also learned how the balance of tap water, as well as how it’s sanitized, can directly impact what you need to do once it’s added to the pool.

If that was all there is to it, water testing would be arguably one of, if not the most, important aspects of water quality management. But these days, what we can do with tests goes so much further.

With today’s automatic testing technology, we can set up systems that will give us a heads up of problems coming our way, and we can use the information we can from that technology to development treatment systems that are resilient to high bather use.

In my own work, I’ve spent years perfecting systems that utilize ozone and UV systems along with very low levels of chlorine residuals. The testing/monitoring systems that accompany that technology are at the heart of everything I’ve done along these lines.

Quite a lot has been made these days of advanced oxidation process. It’s fairly complex chemistry, but in a nutshell, AOP refers to a process where ozone and UV light are combined to create hydroxyl radicals, which are highly oxidative oxygen species that exist in solution for only a tiny fraction of a second. Even though hydroxyl radicals exist for less than a blink of an eye, they are among the most effective oxidizers known to science. Also, because they are so short-lived, it is impossible directly test for their existence. There is no AOP test kit and probably never will be.

RELATED: AOP + Pools: For Some, the Perfect Match

Over the years I’ve learned that you can, however, essentially confirm the existence of hydroxyl radicals by testing the ORP before and after the UV system. As ozone is generated, ORP dramatically increases. When it flows through the UV system, ozone is destroyed and transformed into hydroxyl radicals, which do not register as ORP because of their almost instantaneous reaction time. Therefore, when we see the ORP drop after ozonated water flows through a UV system, we can deduce that the combination of ozone and UV is, in fact, creating hydroxyl radicals.

Making effective use of UV systems also means embracing a couple types of testing that are for the most part unfamiliar to many people in the pool and spa industry. They are two interrelated values known as ultra-violet transmittance (UVT) and ultra-violet absorbance (UVA).

UVT is the measure of how much light passes through a water sample relative to how much light would pass through “pure” water sample, expressed in a percentage. Pure water will have a UVT value of 100 percent, while totally opaque water has a value of 0 percent. The higher the value, the more light is passing through the water, meaning there are lesser concentrations of organics and other compounds that absorb light or disrupt the transmittance.

UVA essentially measures the same thing, but rather than working via transmittance, it measures the relative amount of light absorbed. Both measurements are used to calculate and control the output of a UV system, which in the case of a water treatment system is on the 254nm wavelength.

When you combine, UVT, UVA and ORP testing, you can set up a system that makes the most out of UV and ozone treatment methods. That all might sound like a far cry from standard reagent testing for pH, total alkalinity, calcium hardness and sanitizer demand, but the idea is basically the same. You use testing technology and results to manage the treatment so the system never falls behind the demand on sanitizers and oxidizers relative to bather load and other sources of contaminants.

RELATED: UV — A Sanitizing Assist for Hot Tubs

And in these systems, I’ll use a familiar ppm testing for chlorine for bather-to-bather contacts, as well as pH to maintain balanced conditions. The precise design of these systems and where the different tests are taken in the plumbing depends largely on the situation and I’ll stop short of going into those explanations, which could take up a discussion several times this length.

Suffice to say that how we use water testing has come a long way, but at its core, there is nothing more essential to the successful treatment of water.




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