Fill Water: Basics

In Blog, Chemistry by Cathy Erntson

Fill Water: The Most Important Pool of the Day, Serving It Up Cathy’s Way

We’ve all heard the old saying “Breakfast is the most important meal of the day”. I’m not sure about the validity of that statement, but I can certainly get behind the underlying idea; that everything should start with a good beginning. Pools are no exception. Many of us who work with pools look at the beginning in terms of our day; it all starts with our first set of hand readings. From there we begin the work of pulling the various chemistry parameters where we want them to be; adjusting pH, TA, Cl, etc. Of course, most aquatics professionals have many other tasks as well, but it almost always starts with the pool chemistry, that never-ending circle of test and adjust. But how often do you think about the fill water in this daily cycle? Have you ever tested your fill water?

From the moment we fill a body of water, it already has a certain chemistry to it; Alkalinity, Calcium Hardness, even Chlorine. And since perfect world’s do not exist, these parameters are almost never where you want them to be. These first adjustments made to a newly filled body are usually the largest adjustments we make. (Which makes sense if you think about it, after that first adjustment the chemistry stays within a close enough proximity to where they need to be that we go thru the rest of our days making small as needed adjustments.) On top of all the usual stuff, fill water can also contain vast amounts of all kinds of things we don’t want; nitrates, phosphates, chloramines, etc. I’ve seen countless pools chase chemistry issues due to never realizing that right from go they were starting off with an issue that requires specialty chem treatment. Now, since you would have needed to know what adjustments to make initially, you would have tested the fill water at least that one first time for all the general chemistry parameters. But did you check for metals or nitrates, or combined chlorine? And do you recheck it every time you have to refill that body? It is very common for municipalities to draw from multiple water sources, changing them throughout the year based on need. The water chemistry between these different sources can be HUGELY different, even within the same water district. Even being treated, each water source is affected by the environment around it, making each source chemically unique.

Beyond the initial start-up, our local fill water still plays a significant role in our day to day chemistry; pools constantly lose water and have be topped off. All the more reason to walk over to a faucet and pull a sample once a month, so you know if you are adding potential problems (again, such as metals or phosphates) to the water with your daily top off. If you know your fill water contains stuff it shouldn’t, you can also stay on top of feeding small maintenance doses of specialty chems into the body to make sure the issue can never flare up and become a full-blown issue.

The uninitiated may think a pool is a pool is a pool. But as pool pros, we understand each body of water is as individual as people; each with their own qualities both good and bad! And each requiring its own unique treatment/maintenance plan to stay ahead of the water chemistry game. With the hundreds of chemistry tests we take monthly, It’s always prudent to remember the fill water: “An ounce of prevention is worth more than a pound of cure”.