Now more than ever, plumbing engineers are expected to understand water quality. 

This is important for us to help building owners make decisions if secondary treatment is required. As much as I would like for good, quality public drinking water to be available to everyone, this is not always the case. Even as I savor the subtle differences in tap water from different regions of the country, most people I know tend to reach for the bottle — of water that is. I often lament a poorly functioning drinking fountain, neglected and ignored; or rejoice in a well-functioning one, with a refreshing stream of cool water.

Recently, I helped evaluate different types of water treatment for a project and needed to educate myself with the help of others. Credit goes to all the experts in our field that we count on day in and day out. Over time, I learned a basic understanding of things such as the fact there are minerals in water, and that water should have a relatively neutral pH. I also understand that treatment facilities process water in order to kill bacteria and make it safe, frequently assuring there is residual chlorine. I can usually follow along with the water experts when they start to talk about how all the various properties affect one another. 

This time, I was thrown a curveball. I was reviewing the scenario with a water expert and was following the conversation, nodding affirmatively on my side of the phone, feeling proud of myself for understanding half of what he was saying. Then, he mentioned “dissolved oxygen.” Quite honestly, dissolved oxygen is not something I have thought that much about before. I think our brains are designed to handle maybe three or four parameters, and balance the permutations of how they affect a system. This new, unfamiliar parameter made me feel like hyperventilating into a paper bag in order to balance my own oxygen intake.


The juggling act

As engineers, we balance multiple variables in our decision-making all the time. Sometimes, the more variables there are means there are more possible solutions to a design problem, and we have to sort out all the possibilities to pick the best solution. Understanding water quality can sometimes be like an odds game because small changes can change things so drastically.

External molecules in water typically are referred to in parts per million (ppm). As in turns out, one single part in a million is the same as one milligram in a liter of water (1 ppm = 1 mg/1 L). This is a great example of the convenience provided to us by the metric system. In the spirit of Imperial Units, I propose we call 1 part per million a “speck,” something so small that we can’t see it, but we know it’s there and we can trick ourselves into thinking we see it. Being able to see a speck is like playing the lottery; the odds of us winning aren’t too great, but we can sure imagine ourselves doing so.

Some of the substances we find in water are beneficial and some are not. Chlorine and chloramine, for example, are substances added to water to help “control microbes.” According to U.S. Environmental Protection Agency guidelines (, the maximum contaminant level (MCL) is 4.0 parts per million. This translates into 1 in 250,000, which is about the odds of winning a $10,000 lottery scratch ticket.

Examples of substances that are not beneficial would be things such as arsenic, chromium, mercury or lead. The odds of having these substances in our drinking water is not something we want to see. The MCL for chromium is 0.1 ppm (one “speck” in 10 liters of water), and that of arsenic is another factor of 10: one “speck” in 100 liters of water. Having the maximum level of chromium in our water is on the level of being struck by a falling part from an airplane. 

The point I’m trying to make is it takes an extremely small “speck” in the greater scheme of things to have a large negative effect. Unfortunately, the odds themselves of having contaminants in our water only increase proportional to our lack of vigilance.

Other substances are not necessarily good or bad, depending on how the water is being used or how it affects the piping system. I consider minerals to fall in this category. My understanding is that minerals help keep the pH of water balanced and make water actually taste like water. Just close your eyes and imagine drinking out of a clean mountain stream. Hard water is considered to be water that has a mineral composition of 60 milligrams per liter and greater, or 60 ppm. 

Regarding dissolved oxygen (DO), I think my colleague threw me for a loop because dissolved oxygen is not a solid, per se. It doesn’t necessarily fall into our category of a speck. Dissolved oxygen is the wild card in my poker hand. When I look at how it plays out with the other cards in my hand, the odds become skewed. What treatment systems might increase DO? How does temperature affect DO levels? And how does pressure affect it? Levels greater than 1 mg/L, or 1 part per million of dissolved oxygen is considered corrosive to piping. I also learned bacteria and microbes may multiply with increased levels of dissolved oxygen ( 

By thinking about the odds of events that could happen, it helps lend scale to the effect a speck of something could have on our water. Plumbing and HVAC engineers are becoming more and more dependent upon to understand water quality and how different types of treatment affect water and all the components of the piping network. 

The number of variables we need to balance as we help make engineering decisions can be daunting at times. While we continue to teach our-selves about water quality and work together to investigate water issues that affect the public, we may need to remind ourselves sometimes to take a step back and “just breathe.”