Sump Story: A Radical Change in Make-up Water (with Technical Solution)

A few years ago in the northwest United States, water conditions mysteriously changed at the city-park pool. The chlorine demand seemed to have doubled suddenly, and eyeburn complains increased tenfold. The rate of chloramine development was far greater than before and, while superchlorination would eliminate these unpleasant ammonia compounds, they would always be back the next day. Was the whole swim team relieving itself in the pool during practice in some sort of protest? The pool's aquatic manager didn't really think so…

The usual calls to "experts" yielded no results at all. Then the manager had an idea; he'd phone the local water department and inquire if anything was new or different.

Asked if there had been any changes recently, the water-treatment guy said he didn't think so. "Come on," asked our pool manager, "what's different or new about the water?"

"Nothing, it's still water," answered the man.

After what seemed like several minutes, repeating the question in various forms yet getting the same response, the man from the water department finally said, "Oh, you must mean our new pump. We got it because we put too much chlorine in. See, the state says we have to chlorinate but we can't chlorinate too high – and we were putting too much chlorine in before."

"Why do you need a new pump to put in less chlorine?" asked the pool manager.

"No, no, we still add it like we always did, only now we have the new pump on downstream. It makes our tests come out better, and we use less chlorine."

"What does the new pump do?"

"It does real good, adds that stuff as fast as we can fill the drum!"

"What do you fill the drum with?" was the manager's final question.

"Ammonia."

Ed: Yes, here's a case where knowledge of your make-up water – and maybe the most recent changes therein - is critical for the prediction of trends and for knowing what action is required. Believe it or not, ammonia is – more often than ever before – introduced into the output of our potable-water plants around the country to intentionally make chloramine as the sanitizing agent. It may be a hundred times slower, but there's plenty of time between the reservoir and the kitchen tap. It appears that HOCl has been shown to be mildly carcinogenic, so water districts and controlling agencies have begun to create this odiferous alternative. (Drink a freshly filled glass of tap water at home or in a restaurant and give a whiff; you may understand why, in some communities, the public complains about "too much chlorine" in their drinking water as well as in their pools.) Because people drink city water but don't drink pool water (right?), the move towards avoiding HOCl is related to public tap water, not pool water.

Faced with this problem, some creative solutions have been applied by pool guys. Rather than routinely "maintaining break point" by automating to levels approaching 5 ppm day in and day out, or superchlorinating frequently (and frustratingly), a few pool owners have installed an open-top, well vented holding tank through which the fill water passes. There chlorine is injected, proportional to flow, "on the fly". This affects a real-time, on-line superchlorination process for the fill water. The tank's water is gravity fed with large plumbing to the pool's surge pit. (Important note: The pool controller's sample stream, in this case, must not be tapped in after the circulation pump because the water would not be at all representative of the pool during fill hours. The sample might have to come from a little booster pump tapped into the pool's exit water…)

Another idea for stripping ammonia-bearing fill water, used fairly commonly in Europe, is to pass all the fill water through a relatively large carbon tank (having at least the same volume as the fill-flow per minute). Nearly filled with granular activated carbon – to be replenished regularly – this tank performs miracles in removing unwanted amines and other undesirables.

Another sophisticated solution has been introduced by a major chemical automation company for use with indoor pools. A specialized electronic controller not only feeds chlorine and the pH corrector, it also manages a third chemical, a potassium monopersulfate "enhancer," to preclude the development of chloramines. This system provides a chloramine-free pool, and it helps to improve the air quality in the natatorium as well!

Finally, there is ozone. Unlike potassium monopersulfate, which enhances oxidation but does no sanitizing, ozone excels in both categories. A well-designed ozonation system will destroy both the chloramines produced by the bathers and the "pre-formed" chloramines provided courtesy of the city's potable water plant.

Make-up water has hardness and alkalinity values that need your consideration too, of course. It soon becomes obvious to the trained pool operator that if "you don't know your make-up water, you don't know your pool!"

~kw

© 2002 Professional Pool Operators of America